Update catalog record handling

 * Make catalog record channels use pointers
 * Add connector pointer into metrics
Implement server providers

 * Add new "provider" package
 * Rename former server "origins" into "providers"
 * Make catalog record channels use pointers
 * Move connector query types to "types" package
Merge branch 'providers' of github.com:facette/facette into providers

Conflicts:
	pkg/catalog/catalog.go
	pkg/connector/rrd.go
	pkg/server/library_graph.go
	pkg/server/worker.go