Added texture material and textures, started material texture support

|SOURCE|
[Common/Material]
* Changed the list of MD5s for the textures to a vector
* Added a check for the texture type in the material class, which loads the
  texture for now instead of checking the type and parameters
* GetTextures now returns the array of texture MD5s
[Common/MaterialManager]
* Added LoadTexture, which calls Texture's LoadFromFile and returns the MD5
  digest in the second parameter
* ApplyMaterial also applies the textures in the material
[Common/Shader]
* Added SHADER_PARAMETER_TYPE_SAMPLER_[1,2,3]D
* Added cases for sampler[1,2,3]D in the ExtractUniformNames member function
* Added cases for SHADER_PARAMETER_TYPE_SAMPLER_[1,2,3]D in the
  SetShaderParameter member function
[Common/Texture]
* Added GetDigest
* SetActive accepts a pointer to a Shader which gets used to set the texture
  sampler
[Common/Game]
* Reintroduced the previously commented-out functionality permitting ST
  co-ordinates in the vertex format