OSX: Kdelibs4ConfigMigrator needs to happen after App object is created.

Summary: Calling migrator before the application object was created caused qt platform not to load on OSX, resulting in segfault/abort.

Test Plan:
Verify no longer segfaults on OSX.

@kfunk, I presume that the ConfigMigrator can run after the Application object is created?

Reviewers: kfunk, KDevelop

Reviewed By: kfunk, KDevelop

Subscribers: kfunk, kdevelop-devel

Projects: KDevelop

Differential Revision: https://phabricator.kde.org/D624