Find/Locator: Re-establish initialization order from before the move

Locator's and Find's extensionsInitialized functions were called before
the mainwindow's extensionsInitialized function before the plugins were
merged in one.

Task-number: QTCREATORBUG-11399
Change-Id: I49baac4f9127f75d9650ce11e53327b07775eba0
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>