Move to netty and cleanup

Hi @lukeis,

the change got larger than expected so using this time the pull request mechanism to not break stuff.

The main change is about the move from webbit to netty. There were also some other changes that were needed in order to run the tests. The other changes were mainly about cleanup and test case fixes.

The only thing were I'm not sure that it actually works fine is the screenshot handling. When I use the inspector on the device (e.g. http://localhost:8080/inspector/session/f9374142-55e2-5151-83f6-1b93d109dfcc/ ) the image is displayed correctly. When I use the default inspector on selendroid-standalone (which is using ddmlib for screenshot taking) the images is very small and empty.
On my machine I have the latest android sdk (23.0.2), maybe that is causing issues. The emulator I tested on was platform version 18.

Can you please review the change?

Thanks Dominik