Improved readability
Fixed PluginManager::AddDirectory

Was not adding absolute path
Optimized spot light shader
Added mesh generation of normals and tangents
Added Light::GetLightType
Changed module initialisation behavior
Model::Update no longer skin mesh
Material::Apply now apply shader
SkeletalMesh::Skin now use threads
Added missing const
Fixed MD2/MD5 meshs not having normals/tangents