Git: Support commit.template under ~

Task-number: QTCREATORBUG-9530

Change-Id: I21ee4202aa750a9d4d89f05d51af7c63489eb6c3
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Git: Diff current file against index

Task-number: QTCREATORBUG-9663

Change-Id: I18b4ec5577bf0114075141583c938eaa02d5eded
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>