Added EasyExif in third-party libraries for image I/O purpose and others.
Reviewed architecture of the Graphics module

- Qt implementation is completely hidden using the private
implementation idiom
- Removed some old image display function, which I deemed not practical.
Updated Core module

- Added some color conversion functions
- Rewrote the Timer class
ImageDrawing module updated

- EXIF info parsing using easyexif
- Image I/O for image reading faster than Qt-based image reading (my
implementation is not optimized yet.)
- TODO: image writing, drawing, make Graphics optional.