Prefer local branch name to hash as upstream to pass to Rebase Dialog

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Adjust layout of Rebase Dialog

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Add reverse branch/upstream button in Rebase Dialog

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