Actually upload the contacts to a CardDAV server

This functionality comes from https://github.com/fmarier/gaia/tree/contact-pusher
Remove unused manifest file

It turns out that the manifest file that is used is the one that's
one level up from this one (apps/system/manifest.webapp).
Hardcode the settings for now since through defaults

SettingsHelper isn't able to read any settings at all at the
moment. Let's punt on this by adding default values because we'll
be migrating to an IndexedDB-based solution later anyways.
Add automatic provisioning of accounts with moz.fruux.net

In addition to manually specifying one's CardDAV server and
credentials, it is now possible to automatically provision a
moz.fruux.net account using a Firefox Accounts assertion.

Of course, like any respectable prototype, we don't handle any of
the corner cases and do not check for errors :D

Also, the different providers should probably be refactored into
their own JavaScript files so that we can add more types later.