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/index.js

@@ -1,11 +1,18 @@
 var config      = require("../config/specs");
 var helper      = require("./helper");
 
-require("./util/webdriverio-ext");
-
 
 describe('maputnik', function() {
 
+  before(function(done) {
+    require("./util/webdriverio-ext");
+    helper.startGeoserver(done);
+  });
+
+  after(function(done) {
+    helper.stopGeoserver(done);
+  });
+
   beforeEach(function() {
     browser.url(config.baseUrl+"?debug&style="+helper.getStyleUrl([
       "geojson:example",