Make method naming more consistent.

* Use id() for methods returning a string used to represent
    some type of object.
  * Use displayName() for strings that are meant to be user
    visible.
  * Quieten some warnings while touching the files anyway.
  * Move Factories to their products in the plugins where that
    was not done before.

Reviewed-by: dt

src/plugins/vcsbase/vcsbaseplugin.h

@@ -139,7 +139,7 @@ class VCSBASE_EXPORT VCSBasePlugin : public ExtensionSystem::IPlugin
     Q_OBJECT
 
 protected:
-    explicit VCSBasePlugin(const QString &submitEditorKind);
+    explicit VCSBasePlugin(const QString &submitEditorId);
 
     void initialize(Core::IVersionControl *vc);