Add 'user_from_host' directive to generalize username extraction

Closes #100
Default extractor is backward compatible
Make sure user from domain is always computed locally

Involved upgrade of cartodb-redis to 0.3.0
Really closes #100
cartodb-redis is upgraded to 0.3.0
Merge branch 'develop' into named-maps

Conflicts:
	lib/cartodb/server_options.js
	package.json