VCS: Use documents instead of editors a bit more.

This patch mostly gets rid of EditorManager::openedEditors usage. The
VCS editors should have a better widget<>document separation, also to
make it possible to split/duplicate them, but that's for another time.

Change-Id: Idd92a6a4884ff69fba4f4793d182aa7ff68d79e4
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Fix usage of EditorManager::editorsForFileName

And move to using the corresponding method in document model.

Change-Id: I80b12ceab8a91c5393b9c0422d660a8896ae09d8
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Qbs: Let plugins extend the profiles written into qbs.conf

Provide a way for plugins to extend the profiles that Creator
will write into the Qbs configuration.

This should allow e.g. the Android plugin to add customized settings.

Change-Id: I0de596e2c922280b953c43ea0651b08b8936234c
Reviewed-by: BogDan Vatra <bogdan@kde.org>