Use endpointId option instead of providerId used previously. Used to
access the proxy and also as the key for storing tokens.
Initial working snapshot of OAuth2Connector
  - OAuth2Authenticater is no longer used, as we cannot get the session
and user context required to get hold of the Alfresco connector
  - OAuth2 return webscript now uses endpointId property (configured via
Spring) to scope the storage of tokens
  - Updated path of get and set token webscripts, which can be
overridden in subclasses in getTokenApi() method
  - Get and set token URL webscripts now use URL tokens rather than
parameters
  - Removed the annoying credentials_ prefix previously added by the
vault
Minor update to README
Add chatter-share/target to .gitingore
Use new HttpOAuth2QueryStringConnector connector to load user profile
images. The access token is added on to the URL as a parameter by the
connector.