Pass credential callback on program start

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Add CMassiveGitTaskBase as the base class of CMassiveGitTask

This is to isolate UI class

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Introduce CGit::DeleteRemoteRefs()

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

Conflicts:
	src/Git/Git.h
Call CGit::DeleteRemoteRefs() to delete remote tags

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Call CGit::DeleteRemoteRefs() to delete remote branch

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Merge remote-tracking branch 'remotes/r/libgit2-push'
Workaround cannot operate with keyboard when MenuButton has only 1 entry

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