[Enhancement] Warn when committing with detached head

[Doodeletion]

Commits created while head is detached can easily be lost and are (in my limited git understanding) usually not intended.
It would be nice if SourceGit could display a warning when trying to do this.

There is a very noticable warning about detaching the head when checking out a local commit, but its not that obvious afterwards that the head is currently detached.

Since you can forget about the head being detached or the head could have been detached in a non-obvious way (e.g. submodule updates) it would be nice to have a more visible warning when in the local changes view, so you don't accidentally commit while in detached head state.

[love-linger]

Done.

[Doodeletion]

Thanks!