pgp-zimlet enhancements (from PH-Production)

Medium-sized upgrade converting to OpenPGP 0.8.2 (inc. support for promises) & adding a few features.
(Identical to issue #35 but with 100% less alert() debugging fail!)

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.