Dead drop app

I don't want tp merge this new example app yet, just committing the branch to save it to the repo. This was the test to make sure encryptAndSign actually worked:) 

This example app "DeadDrop" is a very simple message drop application where two users just have to agree on usernames via an alternate channel and they can begin to exchange encrypted messages. 

The messages are removed from the server once they are downloaded, and disappear after the browser tab is closed.

File upload is also a feature this app should support.