Add the Sync & Async plugin implementations.

This starts using the new libusb code.
Fix Peter's comments
Address the last of Peter's comments.
Merge pull request #545 from nomis52/libusb-int

Add the Sync & Async plugin implementations.
Merge branch 'master' of github.com:OpenLightingProject/ola into libusb

Conflicts:
	plugins/usbdmx/AsyncPluginImpl.cpp
	plugins/usbdmx/Makefile.mk
	plugins/usbdmx/UsbDmxPlugin.h