Text search for student feedback form content isn't limited to text content

[etanttila]

Currently the text search filter for student for content searches from everything in the JSON field form_content, including the field names, and content in addition to text, including MCQ responses and time estimates. This sometimes causes problems.

However, this can be difficult to fix, since the names of the text content fields may vary, so one would first need to figure out what are the text fields for each question. Another option would be to separate the response into easier-to-handle format (e.g. splitting it into multiple fields, one for text content and anther for everything else) before saving it in the database (possibly already on the Aplus end before sending it via API).

However, this may be more work than it is worth.

Follows up on issue #42