Scope and purpose

Fixes #3852.

I was uncertain where to put the validation function, so I put it with the forms, but open for better suggestions!

I wish I could have just added a clean method to Room and Location, but DRF does not call that method anymore  when validating (https://www.django-rest-framework.org/community/3.0-announcement/#differences-between-modelserializer-validation-and-modelform), so the API would have anyway had to explicitly call the validation.

How to test:
Go to /seeddb/location/add///seeddb/room/add/ and try to create a room/location with an alias containing the pipe character.

Try to create a location/room with an alias containing the pipe character via the API:

curl -X POST -H "Content-type: application/json" -H "Authorization: Token  sometoken" http://localhost:8000/api/location/ -d '{"id":"Illegal", "aliases":["illegal|"]}'

curl -X POST -H "Content-type: application/json" -H "Authorization: Token  sometoken" http://localhost:8000/api/room/ -d '{"id":"Illegal","location":"locationid", "aliases":["illegal|"]}'

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