rearrange some of the invite link stuff.  This still needs some serious love but we now place emphisis on the link, rather than the email form

and improving admin functionality

Remove partial support for CORS on webfinger routes and replace
it with the Rack::Cors middleware. This provides more complete
CORS support and works around a caching issue with nginx on
Heroku and potentially other reverse proxies.

CORS headers are only added if the incoming request includes
an "Origin" header, which seems to be correct according to
the CORS spec.

closes #2216

improved weekly_user_stats in admin with a dropdown box by week to list all new users of that week also a link_to the user profile so the admin can sent welcome msgs, etc

Users controller small fix; removed the to_activity method and the corresponding tests for status_message model

don't render page-viewer twice; last_post should actually get the last post posted, not the first one

phasing out app.user() for app.currentUser

display proper counts after feedback actions; modified destroy responses to return PostPresenter objects

pjax clicking on nav arrows; move author header into backbone land; comment out comment form for now