[ISS-1111] Add reserved words check to profile registration

[em-wilson]

Resolves Issue-1111: Reserved words - In order to keep nice urls (alonetone.com/sudara) we'd need to create a deny list of reserved words, including anything that might be in routes.rb.

Proposed Changes

1. Adds a helper to check if a username is valid

• Names must not be in use by an account (it's ok if you're already the person using the name)
• Names must not be in use by an account request
• Names must not be part of a DENY list
• Names must not be part of a route, or partial route, provided by the rails application

2. Performs a username check every time someone has an opportunity to change their user name

• When signing up
• When editing their profile
• No difference in user message between valid & taken names is on purpose; I like obfuscating the reason to discourage path stuffing attacks

3. Adds a CRUD screen to add to the deny word list

• Words allow REGEX; it's possible to differentiate between "tomshitfactory" and "expletiveshit" for example