Any feature that's implemented in the UI is implemented as abstraction over things you can do by opening the shell. Because we are a small team that prizes simplicity over completeness, and because GH is the most popular we just made that the default.
But you can open the shell (command/cntrl+k and type "shell") then use git to your hearts desire :)
We'll probably add native GitLab or whatever others want in the future. You can always leave feedback here and tell us what you want: https://repl.it/feedback