theme: use a single function again, call it with 'reset-prompt' action
git: improve current_branch/current_repository

Ref: https://github.com/ncanceill/oh-my-zsh/commit/7f5f8c36f5935b8c3e8a53420d55d195e0ab0774#commitcomment-8782925
Ref: https://github.com/robbyrussell/oh-my-zsh/issues/3363