BrowseRefsDlg: Do not open context menu if user clicks on list header

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fixed issue #2155: Make "Delete Remote Tags..." more discoverable

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Report error to users

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Disable some contradictory options in Clone Dialog

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>