Add a DiffShowEditor showing an additional info

Task-number: QTCREATORBUG-9489

Change-Id: I3ae2e59ccaf397f4236505f21e027a42e2798784
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Petar Perisin <petar.perisin@gmail.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
DiffEditor: Show tooltips with filenames

Change-Id: I32af3b310deb4c96bf1dc798392029cc361ced97
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>