Better handling of tags and roles

[tomcrane]

Currently the tags and roles of assets are stored as comma-delimited strings in a text column in postgres.

We didn't want to tie the schema to Postgres - but we're missing out on the ability to have these as native db array types in postgres:

text[]

...which can be queried on efficiently.

At the very least - tags needs to ESCAPE the , comma character when storing an incoming API array of tags in the single comma-delimited field. It doesn't do this atm!