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

sandbox.config.json

@@ -0,0 +1,5 @@
+{
+  "container": {
+    "startScript": "start-prod"
+  }
+}