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/coreplugin/mainwindow.h

@@ -63,7 +63,6 @@ class SettingsDatabase;
 class UniqueIDManager;
 class VariableManager;
 class VCSManager;
-class IMode;
 
 namespace Internal {