chore(project): verify license headers are present

Closes camunda#1232

Author: nikku

Diff for: .eslintrc

@@ -3,6 +3,7 @@
     "es6": true
   },
   "extends": [
-    "plugin:bpmn-io/es6"
+    "plugin:bpmn-io/es6",
+    "plugin:camunda-licensed/mit"
   ]
 }

Diff for: package-lock.json

@@ -44,13 +44,14 @@
     "electron-reloader": "^0.2.0",
     "eslint": "^5.13.0",
     "eslint-plugin-bpmn-io": "^0.6.1",
+    "eslint-plugin-camunda-licensed": "^0.2.1",
     "eslint-plugin-import": "^2.16.0",
     "execa": "^1.0.0",
     "lerna": "^3.10.8",
     "mocha": "^5.2.0",
     "mri": "^1.1.4",
     "npm-run-all": "^4.1.5",
-    "nyc": "^13.2.0",
+    "nyc": "^13.3.0",
     "proxyquire": "^2.1.0",
     "sinon": "^7.2.3",
     "sinon-chai": "^3.3.0",