Gui: add ShortcutManager to unify shortcut handling

Support longest key sequence match with user defined delay (configurable
through 'Customize -> Keyboard -> Key sequence delay').

Support user defined priority to resolve shortcut conflict through
'Customize -> Keyboard')

Add 'All' category in 'Customize -> Keyboard' to list all command and
showing their shortcuts

Unify macro command shortcut setting (BaseApp/Preferences/Shortcut).

src/Gui/CommandView.cpp

@@ -289,10 +289,13 @@ public:
     const char* className() const override
     { return "StdCmdFreezeViews"; }
 
+    void setShortcut (const QString &) override;
+    QString getShortcut() const override;
+
 protected:
     void activated(int iMsg) override;
     bool isActive() override;
-    Action * createAction() override;
+    Action * createAction(void) override;
     void languageChange() override;
 
 private:
@@ -356,6 +359,19 @@ Action * StdCmdFreezeViews::createAction()
     return pcAction;
 }
 
+void StdCmdFreezeViews::setShortcut(const QString &shortcut)
+{
+    if (freezeView)
+        freezeView->setShortcut(shortcut);
+}
+
+QString StdCmdFreezeViews::getShortcut() const
+{
+    if (freezeView)
+        return freezeView->shortcut().toString();
+    return Command::getShortcut();
+}
+
 void StdCmdFreezeViews::activated(int iMsg)
 {
     auto pcAction = qobject_cast<ActionGroup*>(_pcAction);