This partly addresses QTCREATORBUG-7754: Settings are lost way less
often this way. We do not really want to save whenever settings might
have been touched, so this seems like a good compromise to me.

Most modes at least have some view specific settings that need saving,
so lets just save everything on each mode change. Settings are only
written to disk if they really changed nowadays, so this should be fine.

Task-number: QTCREATORBUG-7754
Change-Id: I26ae18cae38754da6c79a8b870ffae2e681db7c1
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>