Moved USBtoSerial demo the Projects directory, as it is simply an expanded CDC demo. Added const qualifier to Endpoint/Pipe stream write routines.

Move new Class Driver powered demos to a new ClassDriver subdirectory, re-add old low level demos to a LowLevel subdirectory.

Moved out each demos' functionality library files (e.g. Ring Buffer library) to /Lib directories for a better directory structure.

Seperated out OTG, Device and Host mode demos into seperate folders for clarity. Adjusted makefiles so that the path to the LUFA library can be set in one place.