VS Compilation

Updated Jucer project to display libusb.h and getopt.h files in IDE
DfuseLoader.h and FirmwareLoader.cpp inclusion order is very important
because JuceLibraryCode/modules/juce_core/maths/juce_MathsFunctions.h
defines its own ssize_t typedef as libusbx/libusb.h does.
Uncomment of errx() definition in dfu-util/portable.h because it's
needed by VS solutions.
Refactored errx() instance methods to error() in DfuseLoader and
FirmwareLoader files in order to avoid a conflict with
dfu-util/portable.h errx() definition.