add monetized-blog example

[michielbdejong]

• create npm package from Agent class
• create browserified bundle of that
• in-browser: split index.js and make it use Agent class from bundle (how should the bundle drop the LedgerLoopsAgent class into the gobal scope?)
• client-server example: the one currently in master. add some WebSocket robustness using the code from https://github.com/interledgerjs/btp-toolbox/pull/1
• monetized-blog: just tells the browser-extension to send tips to the peer behind a certain WebSocket server