[git]Offer remote selection when pushing from a detached state

When pushing from a detached HEAD state the git greets me with the following error message (which happens with me sometimes when fixing things in git submodules):

fatal: You are not currently on a branch.
To push the history leading to the current (detached HEAD)
state now, use
git push origin HEAD:<name-of-remote-branch>


The command "/usr/bin/git push origin" terminated with exit code 128

 Since the QtCreator already knows the branches available on the pushed remote it would be useful to turn this error message to a dialog where the remote branch could be selected from an UI and in the case if the user approves the selected branch the push could be repeated by the QtCreator itself with the proper arguments.

Since this seems to be a "low hanging fruit" for me if no objections arose I could work on it and submit a patch via gerrit.