Non-rdf resources emit /fcr:metadata events instead of /jcr:content

Fixes https://www.pivotaltracker.com/story/show/81279166
For non-RDF resource /path/to/resource
* updating the content => event on /path/to/resource/fcr:content
* updating the description => event on /path/to/resource

IMHO, both of them should be mapped to /path/to/resource/fcr:metadata, since that is the description for both of them that the message consumer can work with.  If it wants the content (e.g. for fulltext indexing, etc.), then the fcr:metadata will have a pointer to it.