marsharing reshares now grabs the post from the original poster, also fetcheer that person if they don't exist locally still need to ping for xml and give the right xml back

Huge commit I know, but move show and destroy routes into PostsController and PostsController#show into PublicsController

Initial implementation of allowing cross-origin requests in the webfinger flow, so that the unhosted guys can use Diaspora.  May not work with caches-page on host-meta.  We'll have to use X-Accel-Redirect or something.

Remove unnecessary includes, finish renaming set_header_data, only run set_header_data on html requests

This reverts commit 30698d67.