Don't allow empty commits

[joshaber]

Fixes #91

/cc @simurai FYI, so you can Do Your Thing to it whenever you have time.

[simurai]

Added a shake to the editor. But when there are no staged files, the is-required class gets also added to the editor instead of the file list.

If you don't wanna spend more time on this, we can keep it as is (showing the messages only). I think it's fine for now.

[joshaber]

So good.

But when there are no staged files, the is-required class gets also added to the editor instead of the file list.

Ah yeah, I'll make a new issue about that.