Cancel temporary user accounts at the affiliate sites.

#### What's this PR do?
- Cancels temporary users accounts on DoSomething UK

#### Any background context you want to provide?
- There are more than on and a half million users unrelated to DoSomething UK
- To handle this I provided a module update that removes these users in batches of 50
- Criterias I used to determin wheter a user is to delete:
  - User registration source is not `dosomething_uk`
  - User is not an `editor` or `administrator`
- I tested this on my local setup — works perfect

#### How should this be manually tested?
- Enable `dosomething_uk` module
- Patch your source of this PR
- Run Drupal update

#### What are the relevant tickets?
Closes [#DS-411](https://jira.dosomething.org/browse/DS-411).

@aaronschachter in Uk there was a logic based on `user_registration_source`, which is set specifically for UK SSO users. It's not possible to keep this logic for all affiliates, they just don't have this field set. But we can use registration date field with hardcoded release date instead. What do you think?