Moved core files from libs directory to src

src/core/exam/tqatype.cpp

src/core/exam/tqatype.h

src/core/exam/tqaunit.cpp

src/core/exam/tqaunit.h

src/core/exam/tresulttext.cpp

src/core/exam/tresulttext.h

src/core/fonts

src/core/gpl

src/core/instruments/tbandoneonbg.cpp

src/core/instruments/tbandoneonbg.h

src/core/instruments/tcommoninstrument.cpp

src/core/instruments/tcommoninstrument.h

src/core/instruments/tguitarbg.cpp

src/core/instruments/tguitarbg.h

src/core/instruments/tpianobg.cpp

src/core/instruments/tpianobg.h

src/core/instruments/tsaxbg.cpp

src/core/instruments/tsaxbg.h

src/core/minizip/crypt.h

src/core/minizip/ioapi.c