Taxonomy model and data import

[orvn]

We've decided to separate taxonomies, i.e., the definition of allowed categories and tags, into its own file. This will be separate from other settings (see #30 and #43).

Taxonomies need to be created, and then imported based on the actual data we currently have available.

This is a blocker to progress at the moment.

[orvn]

@Ben/@amanda: I’ve populated merged in the taxonomy.json into develop

This is the primary source of truth for category and tag information. If a project specifies a category or tag whose slug does not match the structure in the taxonomy, then that category or tag shouldn’t be displayed.

reference commit and pull/45