Protocol 2.0, now with less kruft

Changes:
* allow batching multiple sensor and touch events in a single message
* stripped out any unused fields and types

Left the Request/Response constructs as it, as alternate names aren't
significantly less annoying as to be worth all the code changes that
would be required.

Change-Id: I5aac47b813096f9b694ffdc81141829ee57336f9