Guild A/B test and Achievement (#8740)

* WIP(guilds): AB test pester modal

* WIP(AB-test): guild pester cont'd

* fix(style): linting error

* fix(AB-test): markModified and notif enum

* fix(tests): update AB expectations

* fix(modal): remove extra includes

* feat(achievements): add Joined Guild cheevo
Also removes unused achievement sprites, and properly saves counter used in A/B testing

* fix(style): linting error from conflict

test/api/v3/integration/user/auth/POST-register_local.test.js

@@ -251,7 +251,6 @@ describe('POST /user/auth/local/register', () => {
         confirmPassword: password,
       });
 
-      await expect(getProperty('users', user._id, '_ABtest')).to.eventually.be.a('string');
       await expect(getProperty('users', user._id, '_ABtests')).to.eventually.be.a('object');
     });