Add basic deletion funcitonality

[pehota]

Add the ability to delete the highlighted branch by pressing d.
It's not possible to delete the current branch.

The functionality is very basic, it just force deletes branches.

[andys8]

Wow, cool.

I'm a bit cautious with deleting stuff. I don't want to make it too easy to avoid it happening by accident. What do you think about some kind of safety prompt?

[pehota]

I am with you on being cautious.
I just thought it might be a good idea to have the functionality in place and then iterate over it by:

1. Adding a propmpt (default behaviour)
2. Shift-d would skip the prompt and delete the branch straight away (for power users 💪)
3. Eventually protect special branches (master, develop) although this is kinda debatable and maybe too much.