Display tags and branches in the revlog

[alexmaco]

fixes #1252

It changes the following:

• adds fg colors to the theme for tags and branches
• displays local branches as labels on their respective commit heads

I followed the checklist:

• [ ] I added unittests
• [x] I ran make check without errors
• [x] I tested the overall application
• [x] I added an appropriate item to the changelog

[alexmaco]

@extrawurst This only displays local branches. Afaict asyncgit cannot report the upstream branch for a local branch, and that info would need to be added to struct LocalBranch, which would remember the name instead of a bool. Should we also do that change?

[extrawurst]

Thank you