Move the code of Pull command to CAppUtils

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fixed issue #1765: Pull button when push (after commit) fails

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Merge branch 'pull-button'
Upgrade libgit2

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Support diff.context config key

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