Initial vehicle API support

This pull request adds a vehicle/ subdirectory which adds initial support for a vehicle api based on the w3c automotive business group draft: https://rawgit.com/w3c/automotive-bg/master/vehicle_spec.html

So far only vehicleSpeed is suported and only the "get()" operation.

Related to (but doesn't completely fix) XWALK-865
This looks like exactly how I had it before.  BTW, I copied the "new" style from the speech extension.  So we already have accepted inconsistencies with our style.  Further, the code checking tool should be updated to catch all this stuff.  Reliance on human checking is a weaker method of style enforcement than a tool.  The tool should be the authority.  If it passes the tool, it's good.