removes unnecessary .then() chaining in test.js as selenium-webdriver already queues calls internally

fixed confusing inverted use of idSelector variable

promisified all tests

promisified test.launchBrowser() and global test hooks

promisified test.closeBrowser()

promisified test.createStandardItems()

🛀 streamlined testOps to always return the promise and flattened out the thens

fixed testOps.assertClearCompleteButtonText() to wait for visible clear-complete button before asserting

fixed testOps.assertClearCompleteButtonIsVisible() to lazy wait for visible clear-complete button

renamed testOps.assertFocussedElementId() to .assertFocussedElement() and streamlined code

fixed page.clickMarkAllCompletedCheckBox() to return inner promise

fixed page.enterItem() to return the promise and flattened out the thens

renamed page.getFocussedElementName() with .getFocussedElementIdOrClass()

fixed page.ensureAppIsVisible() to wait for 'new-todo' element instead of 'main' as some frameworks build the contents after DOM-ready

fixed page.clickClearCompleteButton() to wait for actual button to display before clicking

extracted page.waitForVisibleElement() helper function