Improve the private site login form.  Form now loads inside a vsite context and no longer uses purl_goto, so performance gets a nice bump for private sites.  The form now also properly redirects a user to whatever page they are coming from so if they click on a link somewhere to privatesiste/publications/foo, it will redirect them to publications/foo on login rather than just to the vsite homepage as it previously did.  #2378
Merge branch 'SCHOLAR-3.x' into 2378-improve-privatesite-login
Remove the menu alter for spaces-access-denied as well as the code to pull and alter the user login form.  Just let spacesdisplay the access denied page.  #2378
Update os_url_outbound_alter to redirect the user to a vsite homepage when hitting a private site spaces-access-denied menu entry.  #2378
Merge pull request #2380 from openscholar/2378-improve-privatesite-login

Remove the private site login form.