Plugin Developer Tools: Plugin check & fix tool

Automated tool to discover and fix common plugin faults.

https://mclear.co.uk/2020/07/18/suggestions-for-improving-etherpad-plugins/

- [x] Adds CI and updates existing travis configs.
- [x] Adds a LICENSE
- [x] Adds a .gitignore
- [x] Adds a README and checks it includes a reference to the license
- [x] Recommends translations
- [x] Checks for files that shouldn't exist and removes them (.ep_initialized, npm-debug.log)

still to do in the distant future depending on usage.
- [ ] Check packages.json includes link to github repo
- [ ] Checks Etherpad is referred to as Etherpad Lite
- [ ] Checks README includes animated gif.

bin/plugins/lib/README.md

@@ -0,0 +1,28 @@
+[![Travis (.org)](https://api.travis-ci.org/[org_name]/[repo_url].svg?branch=develop)](https://travis-ci.org/github/[org_name]/[repo_url])
+
+# My awesome plugin README example
+Explain what your plugin does and who it's useful for.
+
+## Example animated gif of usage if appropriate
+
+## Installing
+npm install [plugin_name]
+
+or Use the Etherpad ``/admin`` interface.
+
+## Settings
+Document settings if any
+
+## Testing
+Document how to run backend / frontend tests.
+
+### Frontend
+
+Visit http://whatever/tests/frontend/ to run the frontend tests.
+
+### backend
+
+Type ``cd src && npm run test`` to run the backend tests.
+
+## LICENSE
+Apache 2.0