Indexing of files/custom events

[t3chguy]

Seshat need not conern itself with media but it'd be nice if a client could say oh this media event is actually this blob of text which I fetched from the media store, so index that text as well as the body of the media event (filename).

TL;DR: ability to pass additional terms to index with an event for events which seshat could handle better, e.g media