[PartDesign] Dynamic hole cut-types

‣ Make countersink and counterbore on metric holes freely definable by user.

‣ Fixed the Naming of M1.6, M2, M2.5 and M3.5

‣ Added constructor for custom enums from Enums to PropertyEnumeration

‣ Put definitions of cut-types (counterbore/countersink) for
  screwtypes into json-files for easy modification.

‣ Allow users to put its own definitions in json-files in
  [UserDir]/Mod/PartDesign/Resources/Hole

‣ Contains several examples of cut-type definition json-files that are
  propably not production-ready.

This uses a local copy of nlohmann::json¹ to read json-files.

__________
¹ This is a very nice,header-only C++ library under the MIT License
  (https://github.com/nlohmann/json). I copied the single-file-version
  and the forward-declaration-header into …/PartDesign/App/ so no new
  dependencies arise.

src/App/PropertyStandard.cpp

@@ -329,6 +329,17 @@ void PropertyEnumeration::setEnums(const char **plEnums)
     _enum._index = std::min<int>(index, max);
 }
 
+void PropertyEnumeration::setEnums(const std::vector<std::string> &Enums)
+{
+    if (_enum.isValid()) {
+        const std::string &index = getValueAsString();
+        _enum.setEnums(Enums);
+        setValue(index.c_str());
+    } else {
+        _enum.setEnums(Enums);
+    }
+}
+
 void PropertyEnumeration::setValue(const char *value)
 {
     aboutToSetValue();