Delete entity method and cli

[brrttwrks]

I added a delete-entity method for the AlephAPI class and a corresponding cli command to support a needed operation we are facing not infrequenlty lately and also to learn to support alephclient/tools with a seemingly straight-forward example. Let's see how this goes :).

[stchris]

Sorry @brrttwrks the commit signing thing I sent you was only for the last commit, I didn't pay attention and it seems like you had more of them. But perhaps if you squash all your commits after doing the work and then sign that it should work?