Standardise regex validation
Standardise regex validation

There was a discrepancy between the user sign up field and the admin
profile edit field. Standardise so that usernames uniformly must not use
spaces. This is relevant as profile pages are built using the username,
and it leads to rather messy urls in users create usernames with spaces.

ukgovdatascience/classifyintentsapp,ukgovdatascience/classifyintentsapp