Move check for devices not supporting internal serials in demos which make use of USE_INTERNAL_SERIAL to Descriptors.c from Descriptors.h so that the warning is only generated at most once per compilation.

Set all CDC and MassStorage device mode demos (LowLevel and ClassDriver) to use the USE_INTERNAL_SERIAL feature, add compile time warnings for devices which do not have an internal serial.

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

Deleted StdDescriptors.c, renamed USB_GetDescriptor() to CALLBACK_USB_GetDescriptor, moved ConfigDescriptor.c/.h from the LUFA/Drivers/USB/Class/ directory to LUFA/Drivers/USB/HighLevel/ in preperation for the new USB class APIs.

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.