[Feature request] Narrowing search/autocomplete for branch selection (and other places)

[rzikm]

Currently, user has to write the exact branch name during checkout (or at least I didn't notice any auto-complete/suggestion functionality). Magit uses narrowing search packages like Helm to simplify selecting branch during checkout-branch and other actions. It would be nice to replicate at least some subset of the narrowing search framework in gitu.

[altsem]

I'm considering ripping out the UI for Termwiz.
It does come with a line-editor that has auto-completion mechanisms built in.
However it doesn't seem to be fully compliant when using termwiz widgets (which also seem like a nice addition). Perhaps one approach switching the terminal into line-mode when prompting, and then switching back into raw-mode to rendering the UI.

The UI / Prompt code is a bit of a mess at the moment, and it needs cleaning up before implementing this.