Auto-remove leading/trailing spaces from payloads

[amurphy-cl]

Version where bug was found:
6.1

Describe the bug
Payloads are allowed to have leading/trailing spaces (and possibly other invisible characters), which results in users not getting assigned the appropriate variant. We should automatically remove leading/trailing spaces and hidden characters such as newlines, etc in payloads to prevent this from happening.

[danoswaltCL]

to review from huddle w/ Ben and April on this and related things:

• A hotfix for payloads (perhaps @zackcl 's PR) is appropriate.

To make sure this is something that is handled automagically and never happens again, the frontend and backend should both be trimming / sanitizing hidden characters.

Rather than do this on an input-by-input basis, we should employ broader safety nets on both the Angular side and the Express side. The backend should be the priority as the UI is not the only way bad user input can sneak into a request.

• Backend: We can probably introduce a middleware on backend that can be applied on a controller / endpoint basis to trim and sanitize user input.

• Frontend: We should create a common directive or common utility service that will automatically trim and sanitize user inputs.