Update couch_view to use new couch_event app
[WIP] Update couch_index_server to use couch_event
Add an index committed event
Periodically check if an index should close

We need to periodically check if our index file still exists on disk
because index cleanups don't notify the couch_index process when a file
has been deleted. If we don't check for this condition then the index
can remain open indefinitely wasting disk space.

We make sure that we're idle before closing by looking to see if we
have any clients waiting for an update.
Use ejson_body when opening design documents