Atlas track all textures

[einarf]

Fixed various issues related to texture tracking in atlases.

[einarf]

Remaining:

• Don't raise exception when removing a texture that is no longer in the atlas. This is too error prone.
• Ensure atlas ref is injected into the texture when added every time

[einarf]

• Might need an internal unique_texture counter as well so we don't remove one that has a duplicate
• In addition we need to wrap the add() method so we don't increment the ref coutner multiple times when add() causes a resize or rebuild
• The above point can also be solved by simplifying the clear() method. Splitting it into smaller private methods might be a good idea. The problem is that resize() calls clear with all param flags as false and it's unclear what that even do. We end up wiping texture list, but keep the image ref count.