Added PNG++ source to the tree
Created class Image which loads PNG

`Image` is a simple class that loads a png and stores it. It has width,
height and the raw data. The data is always RGBA tightly packed.
Created macro to delete method

On compilers that support the `= delete` syntax it is used. On msvc,
the method is privated and it's implementation is just a call to abort.
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.
Merge branch 'texture-loading' into development