Fixed issue #874: Add --rebase option to pull dialog

"--rebase" option is introduced by 7f643a07c861c33e48c6fc816e2b34e82df7e736,
but further working is needed.
So, the "Launch Rebase After Fetch" checkbox is hidden from Pull dialog.

For the conflict reason,
the Rebase dialog uses cherry pick(instead of "--rebase" option)
to perform rebase function.
And CLI option "--rebase" should not be used. (never and ever)

Therefor, if "Launch Rebase After Fetch" checkbox is checked in Pull dialog,
then "git.exe pull --rebase" is adapted to "Fetch & Rebase".

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