Fix on png++
Created Texture class

A Texture is created from a Image. It may be set over a sampler2D
uniform.
ProgramContext supports bool uniforms
Added method to drawTexture on OpenglContext

The method draws a texture in a box shape. The shape is the same used
on drawBox
Showing an image on the main application
Uninverted image and alpha support

The image is loaded inverted so it works correctly according to OpenGL
coordinate system.
Also, alpha blending was enabled on the OpenGL setup.