Encrypt user data (messages, contacts, etc.)

[ajstensland]

Probably want to:

1. Create random session key
2. Encrypt data with session key
3. Encrypt session key with public key
4. Store session key

This will result in considerable lag upon load_contacts and save_contacts calls.

Most likely points to a reworking to make contacts an instance variable. Edit: Nevermind this point -- if contacts were stored in an instance variable it'd be the same amount of work to update it from slyther-server calls.