#14 Improve customization

[AndreLDM]

Reference: fltk/test/input.cxx:58
Remove all unnecessary code which sets the color for some specifis widgets and do as in the reference.
See attachment for a better understanding.
This way KISS Player can be fully customizable(at least in terms of color).
The only problem is that the buttons icons are png image on memory and to tint them on the run seems very trick.

[AndreLDM]

Moved to GitHub:
https://github.com/andreldm/kissplayer/issues/10