* add google+
* sort signin oauth2 providers based on the name so order is always the same
* update auth tip for google+
* add gitlab provider
* add bitbucket provider (and some go fmt)
* add twitter provider
* add facebook provider
* add dropbox provider
* add openid connect provider incl. new format of tips section in "Add New Source"
* lower the amount of disk storage for each session to prevent issues while building cross platform (and disk overflow)
* imports according to goimport and code style
* make it possible to set custom urls to gitlab and github provider (only these could have a different host)
* split up oauth2 into multiple files
* small typo in comment
* fix indention
* fix indentation
* fix new line before external import
* fix layout of signin part
* update "broken" dependency
* initial stuff for oauth2 login, fails on:
* login button on the signIn page to start the OAuth2 flow and a callback for each provider
Only GitHub is implemented for now
* show login button only when the OAuth2 consumer is configured (and activated)
* create macaron group for oauth2 urls
* prevent net/http in modules (other then oauth2)
* use a new data sessions oauth2 folder for storing the oauth2 session data
* add missing 2FA when this is enabled on the user
* add password option for OAuth2 user , for use with git over http and login to the GUI
* add tip for registering a GitHub OAuth application
* at startup of Gitea register all configured providers and also on adding/deleting of new providers
* custom handling of errors in oauth2 request init + show better tip
* add ExternalLoginUser model and migration script to add it to database
* link a external account to an existing account (still need to handle wrong login and signup) and remove if user is removed
* remove the linked external account from the user his settings
* if user is unknown we allow him to register a new account or link it to some existing account
* sign up with button on signin page (als change OAuth2Provider structure so we can store basic stuff about providers)
* from gorilla/sessions docs:
"Important Note: If you aren't using gorilla/mux, you need to wrap your handlers with context.ClearHandler as or else you will leak memory!"
(we're using gorilla/sessions for storing oauth2 sessions)
* use updated goth lib that now supports getting the OAuth2 user if the AccessToken is still valid instead of re-authenticating (prevent flooding the OAuth2 provider)
