Styling chat bubbles

CSS for 'own' and 'other' chat bubbles. This is managed with some clever
positioning and rotation of borders. Colors and sizes are all TBD.

Minor tweaks to the JS to enable this. The message is now returned from
decrypt/verify functions as an object, where message.message contains
the content (which formerly was the entire return value) and
message.trust contains the MessageAuthenticated enum value.

I likely will add further styling for messages that could not be
decrypted, and for messages where the signature could not be verified.

Chat identity

The chat app now uses digital signatures for identify verification.

A new blog post discusses this implementation and what I've learned
about PGP and digital signature cryptography.

Also, minor typo fixes and adding an aspell recipe.