Add pattern validation to slug fields

At least in

* survey slugs (dash)
* dimension slugs (underscore)
* dimension value slugs (underscore)
* form field slugs

Currently this is the validator used in backend:

https://github.com/con2/kompassi/blob/69c3418ab4da651f6eab9c2890c60076b29f7623/backend/core/utils/model_utils.py#L9-L12

However, this is not validated on the forms, causing a GraphQL error and #399.

Add a similar pattern validator in the frontend to the inputs that convey slugs.

Also the backend validator is shit and does substring match or something else that is fucked up. For example `ooh-tukilomake ` including the space is a valid survey slug according.