Vastly improved contact creation, WA notify tracking

- Instead of contacts/recipients potentially being created in like
  three disparate places, there is now one and only one place
  where this happens: the object responsible for the protocol,
  i.e. the WhatsApp or modem manager.
  - This makes everything far simpler, and means we can actually
    keep track of things like contact names properly, instead of
    wondering which part of the bridge will end up making the
    contact in the end.
- All of the WhatsApp contacts we get on the initial burst, and
  any added thereafter, are now translated into recipients.
  - In addition, we keep track of their 'notify' property (i.e.
    the ~tildename for each contact, or the contact name from the
    user address book), and store that in the database.
  - In future, the bridge will perhaps let you autoname people,
    or display their notify in some meaningful way to allow you
    to differentiate people amongst the sea of random numbers...