Enable "Pick Branch" checkbox only if normal rebase is possible

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Add tooltips to Pick Branch checkbox

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
the rest changes after Make_pot.bat, might be dropped?

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>