Added olympic.png images.
Added texture to the net.
Chagnes:
 * added stone texture
 * now user can turn on/off linear texture filtering with key 'L'
 * added new structure gk3d::RenderParams, which should be given as parameter in ModelInstance::Render
Changes:
	* added mimmap
	* user can turn on/off trilinear texture mimmap filtering with 'T' key
	* added min and mag filter's parameters to gk3d::RenderParams
Changes:
	* now user can change GL_TEXTURE_LOD_BIAS param with 'P' and 'O' keys.
Changes:
	* enabled mutitexturing mode
	* user can change court's material with 'M' key
Changes:
	* added fog (3 equations)
	* user can turn on/off(change diff equations) fog with 'F' keys, change fog density with 'G' and 'H' keys
Gotowe zadanie 1,2,3,5.