Consider using `git-switch` instead of `git-checkout`

**Is your feature request related to a problem? Please describe.**
It seems like currently gitui uses a command similar to [`git-checkout`](https://www.git-scm.com/docs/git-checkout) when changing branches or creating new branches. This has the drawback of not handling cases where there are uncommited changes in the working tree. (This is just the example I most commonly encounter. From what I gathered [`git-switch`](https://www.git-scm.com/docs/git-switch) is generally more versatile)

**Describe the solution you'd like**
I would like gitui to use a command similar to [`git-switch`](https://www.git-scm.com/docs/git-switch) when changing branches. This would allow me to change branches even if there are changes in the working tree.

**Describe alternatives you've considered**
Currently I exit out of gitui and run `git switch` manually from the command line.