Do not switch to original commit of upstream branch at the beginning and end of rebase

This reduces making working dir files dirty

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Rebase Dialog: Fix selected wrong upstream if it is a branch name

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Prefix local branch name to hash 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>