Bug 918012 - Sync with FxAccount and token server. r=rnewman
Bug 899217 - Part 1: Register about:accounts code. r=rnewman

This is temporary code for our first engineering milestone.  I know of
the following issues:

* the page doesn't implement the full interface and spec that the
  loaded content expects; it just does enough to work.
* logs are repeated if about:accounts is re-loaded.
Bug 899217 - Part 2: Connect about:accounts to FirefoxAccountsHelper. r=rnewman