WIP commit for facebook v2.2
Don't guard against undefined reference
Implement javascript side of native plugin
Support multiple listeners for native events

Native events are proxied in javascript to get around the one subscriber
limit. All of the facebook events can be subscribed to, but not all of
them are supported by the native code.
Start on iOS native
Update facebook SDK to latest version
Initial support for iOS

iOS is ready for alpha users. There are some definite issues with
`FB.api` on this platform at present.
Add log.h to iOS
Add latest facebook sdk
javascript native wrapper parses json strings

The android plugin interface modifies json objects passed to
sendRequest. Strings are passed through unmodified.
Implement native backing on android

The JavaScript methods

    FB.api
    FB.ui
    FB.login
    FB.logout
    FB.getAuthResponse
    FB.getLoginStatus
    FB.init
    FB.Events.subscribe (core events only)
    FB.Events.unsubscribe

are now backed on native-android. Error responses are likely to not
match the JavaScript SDK, but the api results should be identical.

Android support for facebook v2.2 can now be considered **alpha**
quality - that is, bugs are likely, but everything mostly works.
fix iOS login scope handling

This method now expects the correct type for the `scope` parameter.
Remove unused dependency
Document native FB.login api difference

Native can only request read permissions during initial login.
Fix android manifest xsl injection

The keys are now properly pulled from the manifest.json addons.facebook
section.
Fix android login `scope` interface
Fix android error bubbling in some cases

Errors such as "invalid key hash" now properly bubble up to JavaScript.
Fix android multiple initializations

Moves initialization logic and event trigger to `onCreate`
Add frictionless request support on iOS

The `frictionlessRequests` flag to FB.init is now effective on iOS.
Frictionless requests do not seem to be supported on android at the
present time.

Resolves #16
Add "fb" interpolation string to plist urlscheme

devkit-core v2.0.15 fixed an issue where string interpolation did not
work. This allows us to generate the url scheme automatically from the
application id.

Resolves #13.