Allow dataclip body to be searched as text (tsvector)

[christad92]

We recently added a gin index to dataclips.body, however the search query is treating the body as a string.

In order to use a gin index on a JSONB type, the query should use a json operator (@>, @@, @?...).

So in order to search dataclips as text (and be performant), we need to:

1. Cast the json as a tsvector
   Attention should be paid as to the dictionary choice to ignore JSON syntax.
2. Store the vector in a new column (body_search_vector?)
3. Add a GIN index to the new column.
4. Change the history page query to use the search vector instead of casting the body as a string.

NOTE: re: dictionary choice, we need to make sure that this accommodates a variety of searching patterns - please can we document at least 5 varying json document structure and/or search string variations. With tsvector it's entirely possible that compound words (camelCase) and other "not English words" might be ignored.