Drop /map_metadata API entry point

Closes #101
Revert "Drop /map_metadata API entry point"

This reverts commit b37b07a06a1dd3cf05d60f4aa613ab5c48b90700.

This was too light of a decision...
Drop the idea that we can distinguish a "dbowner" from the domain

We only recognize "users"
Merge branch 'develop' into named-maps

Conflicts:
	lib/cartodb/server_options.js