Clef for WordPress 2.0

Clef for WordPress 2.0 is coming!

TODO:
- [x] Set logout hook explicitly to wp-login.php URL
- [x] Fix issue where if user login fails and they reload the page, they see another error (caused because OAuth code is in URL bar)
- [x] Review authentication-checks for all places where settings changes occur
- [x] Badge notification sometimes doesn't add badge
- [x] Invite users message displayed incorrectly (https://www.dropbox.com/s/3dbwkvqmj2ao9m9/Screenshot%202014-02-13%2009.23.55.png) [FIXED by adding clear: both to element)
- [x] Ensure that all displayed strings are wrapped in `__($string)` or `_e($string)` for i18n
- [x] Gracefully educate Clef users in Google Chrome about Waltz
- [x] Add Invite Users as a tutorial step
- [x] Add error messages to settings
- [x] Ensure that multisite settings work as well as single-site settings
- [x] Make an option on the settings page to invite site users to Clef
- [x]  Add `wp_nonce` to invite users action
- [x]  Stop redirecting to Edit Profile upon clicking of invite link and redirect to custom tutorial page instead
- [x] Restructure plugin for modularity, so that it is more self-contained and can be included with ease in various places
- [x] add html for badge and link
- [x] fix disappearing connect clef account