Kaiju Engine (issue #51 & #52) - Improve the GL drawing of instances

This makes it so that shaders are only bound once and will draw all of the instances that are bound do them. This also fixes an issue of re-generating the texture every frame for draw instance groups instance data. The texture is now re-crated only when the group expands.

https://github.com/KaijuEngine/kaiju/pull/54