Ability to edit and save "Thresholds"

[aninek]

Purpose:
Recognizing that standard approaches may not reflect local realities, Data owners may need to allow teams to change the pre-filled Threshold for a health risk. We are interested in:

• Allow user to select "Edit"
• User selects form field and can rewrite the [Case definition]
• User must record a reason why the [case definition] is being changed (comment field)
• System records; new case definition (without overwriting original), timestamp, user details, project affiliation, and comment.

Related to #54 and #59

[karolikl]

Fixed by #278

[eprom]

@aninek Could you define what a "user" is since this involves access control and authorisation.