VCS: Do less when command is aborted internally

If the user cancels a command, output and error text might still be
interesting. When aborting a command internally (when Creator is closed,
or later when a command is re-executed for the same editor), we don't
want any of those, and they have a destructive potential.

Change-Id: I5e35fdf59c0fcdc0af45f13ac142da31edf18bd7
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
VCS: Abort previous command for the same editor

It is very common to have output from a previous (longer) command appear
instead of the newly created one.

For example: Open a log. Check "Show Diff" and immediately uncheck it.
If this is done fast enough (or with a high Log Count limit) the output
with the diff will appear instead of the normal log.

Change-Id: Ie64cc4a383a261f5328a4d0486eec93f73766679
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Git: Remove setting for side-by-side diff

Use the diff switcher state as a permanent setting

Change-Id: I6c3669090082787ae750596cf3e62973c04d94c3
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Git: Set default button for change-related actions by triggering action

Change-Id: I536618e9b80f3ed213c6c54dd6c2becbb64c709b
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>