Added new CI workflow using GitHub actions.

Also

 - Fixed screenshot tests
 - Fixed code coverage
 - Removed appveyor
 - Removed circleci
 - Updated wdio related dependencies
 - Added docker image deploy to the GitHub registry

test/functional/util/coverage.js

@@ -14,7 +14,9 @@ afterEach(function() {
     return window.__coverage__;
   });
 
-  coverage.merge(results.value);
+  if (results) {
+    coverage.merge(results);
+  }
 })
 
 // Dump the coverage to a file