Fix bug 948041 - "Is basket working?" management command

New command is "manage.py check_basket"
[fix bug 969039] Change moderated group's join notification.
[fix bug 973387] Allow curators to change accepting_new_members field.
Merge pull request #766 from caktus/948041-is-basket-working

Fix bug 948041 - "Is basket working?" management command
[fix bug 979837] Add Mozilla Webmaker to External Accounts
Merge pull request #851 from mishravikas/fix_979837

[fix bug 979837] Add webmaker to External Accounts
[fix bug 930999] Add username_not_url validator to external accounts.

Refactor username_not_url validator

Simplify username validator

Change _lazy to _

Simplify username_not_url
[bug 930999] Add ExternalAccountForm tests.
[fix bug 979828] Add Mozilla Wiki to External Accounts
[fix bug 968945] Add proper messaging when no open membership requests
Merge pull request #853 from mishravikas/fix_968945

[fix bug 968945] Add proper messaging when no open membership requests
Merge pull request #852 from ssbl/mozwiki

979828 - Add Mozilla Wiki to external accounts
[fix bug 972466] Add styles to group edit submit button.
Merge branch 'buttons'
[fix bug 979203] Clean up external account data
Merge branch 'jpotts-fix_979203'
[bug 979203] Don't change ExternalAccount on dupe.
[fix bug 983100] Do not auto-add people to staff group.
Merge pull request #856 from glogiotatidis/delete-staff

[fix bug 983100] Do not auto-add people to staff group.
[fix bug 983218] Remove 'url' from Website External Account.

Website External account doesn't need a 'url'. With 'url'
ExternalAccountForm.clean will try to clean it and it'll remove trailing
/.