SpaceFN layout implementation.

Added support for multilayer layouts with dual function keys.
Moved layouts into PROGMEM.
CuTest based unit tests.
Plain-vanilla SpaceFN layout implementaton:
  http://geekhack.org/index.php?topic=51069.0

    modified:   Makefile
    modified:   hw_interface.c
    modified:   lib/keycode.h
    modified:   main.c
    new file:   logic.c
    modified:   models/common.h
    new file:   test/AllTests.c
    new file:   test/CuTest.c
    new file:   test/CuTest.h
    new file:   test/KbdTest.c
    new file:   test/TestLayout.h
    new file:   test/license_cutest.txt
    new file:   binaries/flake_SPACE_FN.hex