arrow keys should navigate while in commit edit window.

[shidel-dev]

When I am editing a commit, I am not able to navigate via the arrow keys. If a want to fix a misspelled word I must use backspace.

[golbin]

I've finding a proper solution. We can using https://github.com/slap-editor component but it's very big project than GC. So, maybe I need to implement cursor behavior simply.

[golbin]

I made a patch of blessed for this. chjj/blessed#156

When this patch will be approved, it'll be fixed.