Added functional test for uploading image/cover in settings

references #2273
- added a test that clicks on both upload (image/cover) buttons and tests the same testing function on them since both modals are exactly the same
- the testing function checks for the '.js-drop-zone.image-uploader' selector, then clicks accept, and tests that a blank success notification appears
- shifted the test email test validation upwards so the ordering of tests matches the ordering of the UI elements