Mastodon Git UI Improvements

[maarzt]

• The switch branch command show branches as strings "refs/head/main" etc. This is overly technical. Shorten the string to "main"
• When a pull fails due to a merge conflict, allow a user to put the local changes into a local branch maybe called "stash" ...
• Have a window that shows a branch history like gitk, and allows to switch between branches.