Fix "menurebase.ico" in order to display properly in Settings dialog

(fixes issue #2124)

Signed-off-by: Ricardo Alexandre Vieira <vierinha@gmail.com>
Signed-off-by: Sven Strickroth <email@cs-ware.de>
Update "Push.ico" to look more similar to Pull and Commit icons

Signed-off-by: Ricardo Alexandre Vieira <vierinha@gmail.com>