Distinguish *->t functions that return tags only

Defines *->t+b functions that return a map of tags as keys associated to
their entire set of behaviors (as used by browser filter-lists).

 *->t functions only return a sequence of tags.
Use  to create sets
Review docstrings
Store behavior arguments as kv rather than metadata

When a tag passes arguments to a behavior, they will be stored as kv
`:lt.plugins.aleph.bot/args` in the list produced by `t->b`.
Use reviewed & namespaced BOT relation functions
Define functions to search behaviors by triggers
Define functions to search objects by id