ES6 all the things

• adapter is now using ES6. This is a major change and probably broke stuff
• navigator.getDisplayMedia shim is gone. Only navigator.mediaDevices.getDisplayMedia survives.
• getStreamById is gone from Safari shim. It is gone from Chrome too.
• removed lots of cruft from Chrome and Firefox shims. If you need support for browsers which are older than two years stick with the old version