FGDC Topic Category extraction
Assigns TopicCategory to Layer using extracted metadata.
Added category_list to advanced search context for category filter
Added category filter
Added support for capturing multiple keywords from FGDC metadata.
added OL to search
added UI for search by extent
UI cleanup for extent search
added extent filter to search results page
Refactoring migrations.
Added the migration for adding the resourcebase_ptr_id field in layer.
Added the migrations to move layer stuff to base.
Some more steps added.
removed extra openlayers in favor of OL wrapped in ExtGeo
added geoexplorer JS packages in search templates and wrapped in Ext
Improve security for the proxy view.  Fixes #1308.

* In production, the proxy will only respond to hosts  listed in the settings.PROXY_ALLOWED_HOSTS tuple and the OGC_SERVER hostname.

* Remove the pass through authentication headers.  Pass through authentication headers were getting added to requests outside of their respective realm.

* Add a PROXY_URL setting so administrators can use proxies other than the GeoNode.

* Only forward session cookies to the OWS url since commit ef1cf1 states that session cookies can influence local OWS GetCapabilities requests.
Merge pull request #1315 from garnertb/proxy

Improve security for the proxy view.  Fixes #1308.
Updated changelog for version 2.0c7
add missing double quotes in layer detail
add missing slash in proxy url