Replace Travis with Github actions

Two workflows have been added,

  * PHP build - Runs tests on version 7.2, 7.3, also runs phpcs
  * Node.js build - Runs tests on version 8.x, 10.x, 12.x, also
    runs ESLint

Bug: T218639

package.json

@@ -36,6 +36,7 @@
   },
   "license": "GPL-2.0-or-later",
   "scripts": {
-    "test": "mocha tests/js/*.js"
+    "test": "mocha tests/js/*.js",
+    "lint": "eslint src/*.js"
   }
 }