Metatag paths

This is very much a sandbox module, but will (hopefully) go on to provide path-based metatag management for the metatag module.

Currently it's largely a re-named version of the Beanstag sandbox. As such, it uses its own database table and has no integration with metatag module. I hope to switch that out to use the metatag module api instead, at which point this becomes it's own thing and not just a renamed Beanstag