Adding end-to-end tests

The first test is testing a tricky cache scenario with the back when testing variables.
The end-to-end package used is testcafe.

maps/tests/Variables/Cache/script.js

@@ -0,0 +1,5 @@
+WA.onInit().then(async () => {
+    console.log('Trying to set variable "myvar". This should work, even if the cache was busted.');
+    await WA.state.saveVariable('myvar', {'foo': 'bar'});
+    console.log('SUCCESS!');
+});