Allow changing facebook parser and change default parser to json

[tg90nor]

With Facebook deprecating version 2.2 of the Graph API, they now only return json access tokens.

See https://developers.facebook.com/docs/apps/changelog

[Oauth Access Token] Format - The response format of https://www.facebook.com/v2.3/oauth/access_token returned when you exchange a code for an access_token now return valid JSON instead of being URL encoded. The new format of this response is {"access_token": {TOKEN}, "token_type":{TYPE}, "expires_in":{TIME}}. We made this update to be compliant with section 5.1 of RFC 6749.

[joshbuker]

Going to use this PR to work on the facebook issue (and pull the relevant changes out of #51 and into here).

Closes #52

[joshbuker]

Tested this on athix/sorcery: testing/facebook-fix; should fix facebook without action (beyond updating to this version of sorcery) and allows setting parse for facebook via config.

[joshbuker]

@Ch4s3 can you review / merge and release this pull request ASAP? Fixes users being unable to login via Facebook using Sorcery.

[5hanth]

@Ch4s3 @athix : guys! would be great if this is reviewed and merged ASAP.. thanks!

[joshbuker]

Merging this into master, @Ch4s3 can you please cut a new release (0.10.4) when you get a chance?

[danReynolds]

If someone could cut a new release it'd be great to get this working on master. Thanks!

[joshbuker]

@danReynolds currently only @Ch4s3 has the ability to cut a new release, still waiting to hear back from them.

Released