Fix default shortcut for git commit

Still works in 3.2, broke with ae844bdf9e9fa24fa4ad9986b93d2399c7676c01

Change-Id: I3ff806c299baef5ff8ada393e4934244064e81e6
Reviewed-by: hjk <hjk121@nokiamail.com>
TextEditor: Centralize settings connections setup

All editors did that manually, with varying approaches. Connect once
when the document is made known to the EditorWidget instead.

Change-Id: Ib0828b08158539859f6f89c8080435a027aa06ed
Reviewed-by: Christian Stenger <christian.stenger@digia.com>