pgp-zimlet enhancements (PH Production)

Medium-sized upgrade converting to OpenPGP 0.8.2 (inc. support for promises) & adding a few features.

Major Enhancements:
- Support encrypting to multiple recipients. - Issue #16 
- Support storing Private Key on server.
- Support storing Private Key Passphtrase on server.
  Use of this feature is STRONGLY DISCOURAGED, might remove it in the future.

Major Changes:
- OpenPGP.JS 0.8.2 (Promises Promises Everywhere)

Minor changes
- Take advantage of openpgp.js functions that take lists of keys, by passing lists of keys.