Add support for git worktrees

[Mingun]

Is your feature request related to a problem? Please describe. I use worktrees a lot. Currently Gitnuro shows an error in an attempt to open worktree working copy. For example, GitKraken also does not support worktrees, but it at least can open it as a separate git repository. Gitnuro, however, just shows the error:

Submodule's parent repository not found

Describe the solution you'd like Add ability to work with worktree working copies created by git worktree command

Describe alternatives you've considered None