[Engine] Updated documentation.
[Engine] Renamed ColorVertex to VertexType and added UV data members.
[D3D11Renderer] Renamed VertexType to D3D11VertexType.
[D3D11Renderer] Created TextureMaterial class which will handle rendering textured meshes.
[D3D11Renderer] Removed unneeded color input layout entry for TextureMaterial.
[D3D11Renderer] TextureMaterial is now initialized on startup.
[Engine] Added interface functions for loading textures.
[D3D11Renderer] Implemented texture loading and texture shading.