Add two options to disable addons

Addons can be disabled in two ways:
 * by adding a command line argument `--disable-addon <addon>`
 * and by creating a `ALL_ADDONS_DISABLED` file in the mod root of the addons to disable

src/App/Application.cpp

@@ -2250,6 +2250,7 @@ void parseProgramOptions(int ac, char ** av, const string& exe, variables_map& v
     ("run-open,r", value<string>()->implicit_value(""),"Run a given test case (use 0 (zero) to run all tests). If no argument is provided then return list of all available tests.  Keeps UI open after test(s) complete.")
     ("module-path,M", value< vector<string> >()->composing(),"Additional module paths")
     ("python-path,P", value< vector<string> >()->composing(),"Additional python paths")
+    ("disable-addon", value< vector<string> >()->composing(),"Disable a given addon.")
     ("single-instance", "Allow to run a single instance of the application")
     ("safe-mode", "Force enable safe mode")
     ("pass", value< vector<string> >()->multitoken(), "Ignores the following arguments and pass them through to be used by a script")
@@ -2431,6 +2432,16 @@ void processProgramOptions(const variables_map& vm, std::map<std::string,std::st
             Base::Interpreter().addPythonPath(It.c_str());
     }
 
+    if (vm.count("disable-addon")) {
+        auto Addons = vm["disable-addon"].as< vector<string> >();
+        string temp;
+        for (const auto & It : Addons) {
+            temp += It + ";";
+        }
+        temp.erase(temp.end()-1);
+        mConfig["DisabledAddons"] = temp;
+    }
+
     if (vm.count("input-file")) {
         vector<string> files(vm["input-file"].as< vector<string> >());
         int OpenFileCount=0;

src/App/FreeCADInit.py

@@ -106,6 +106,7 @@ def InitApplications():
     MacroMod = os.path.realpath(MacroDir+"/Mod")
     SystemWideMacroDir = FreeCAD.getHomePath()+'Macro'
     SystemWideMacroDir = os.path.realpath(SystemWideMacroDir)
+    DisabledAddons = FreeCAD.ConfigGet("DisabledAddons").split(";")
 
     #print FreeCAD.getHomePath()
     if os.path.isdir(FreeCAD.getHomePath()+'src\\Tools'):
@@ -218,11 +219,30 @@ def InitApplications():
         except Exception as exc:
             Err(str(exc))
 
+    def checkIfAddonIsDisabled(Dir):
+        Name = os.path.basename(Dir)
+
+        if Name in DisabledAddons:
+            Msg(f'NOTICE: Addon "{Name}" disabled by presence of "--disable-addon {Name}" argument\n')
+            return True
+
+        stopFileName = "ALL_ADDONS_DISABLED"
+        stopFile = os.path.join(Dir, os.path.pardir, stopFileName)
+        if os.path.exists(stopFile):
+            Msg(f'NOTICE: Addon "{Dir}" disabled by presence of {stopFileName} stopfile\n')
+            return True
+
+        stopFileName = "ADDON_DISABLED"
+        stopFile = os.path.join(Dir, stopFileName)
+        if os.path.exists(stopFile):
+            Msg(f'NOTICE: Addon "{Dir}" disabled by presence of {stopFileName} stopfile\n')
+            return True
+
+        return False
+
     for Dir in ModDict.values():
-        if ((Dir != '') & (Dir != 'CVS') & (Dir != '__init__.py')):
-            stopFile = os.path.join(Dir, "ADDON_DISABLED")
-            if os.path.exists(stopFile):
-                Msg(f'NOTICE: Addon "{Dir}" disabled by presence of ADDON_DISABLED stopfile\n')
+        if Dir not in ['', 'CVS', '__init__.py']:
+            if checkIfAddonIsDisabled(Dir):
                 continue
             sys.path.insert(0,Dir)
             PathExtension.append(Dir)

src/Gui/FreeCADGuiInit.py

@@ -192,11 +192,31 @@ def InitApplications():
         except Exception as exc:
             Err(str(exc))
 
+    def checkIfAddonIsDisabled(Dir):
+        DisabledAddons = FreeCAD.ConfigGet("DisabledAddons").split(";")
+        Name = os.path.basename(Dir)
+
+        if Name in DisabledAddons:
+            Msg(f'NOTICE: Addon "{Name}" disabled by presence of "--disable-addon {Name}" argument\n')
+            return True
+
+        stopFileName = "ALL_ADDONS_DISABLED"
+        stopFile = os.path.join(Dir, os.path.pardir, stopFileName)
+        if os.path.exists(stopFile):
+            Msg(f'NOTICE: Addon "{Dir}" disabled by presence of {stopFileName} stopfile\n')
+            return True
+
+        stopFileName = "ADDON_DISABLED"
+        stopFile = os.path.join(Dir, stopFileName)
+        if os.path.exists(stopFile):
+            Msg(f'NOTICE: Addon "{Dir}" disabled by presence of {stopFileName} stopfile\n')
+            return True
+
+        return False
+
     for Dir in ModDirs:
-        if (Dir != '') & (Dir != 'CVS') & (Dir != '__init__.py'):
-            stopFile = os.path.join(Dir, "ADDON_DISABLED")
-            if os.path.exists(stopFile):
-                Msg(f'NOTICE: Addon "{Dir}" disabled by presence of ADDON_DISABLED stopfile\n')
+        if Dir not in ['', 'CVS', '__init__.py']:
+            if checkIfAddonIsDisabled(Dir):
                 continue
             MetadataFile = os.path.join(Dir, "package.xml")
             if os.path.exists(MetadataFile):