Task-number: QTCREATORBUG-731

Used the wrong indexes, set focus option.

Give dialogs a consistent look, set
WA_DeleteOnClose on them and improve updating.
Add a Refresh/Diff buttons to branch dialog.

Add non-modal stash management dialog and additional menu option
"Stash snapshot..." to stash away changes prompting for a description,
which will immediately replay the stash (take snapshot and continue
working).
Add interface to IVersionControl for creating/restoring/deleting
snapshots for backup/complex undo operations (currently supported
by git only). Add test options to VCSBasePlugin.
Clean up and extend git client accordingly.