This adds the copy method to our types

All our basic types except models have the copy method.

 - `PointCloud`
 - `TriMesh`
 - `TexturedTriMesh`
 - `ColouredTriMesh`
 - `Image`
 - `BooleanImage`
 - `MaskedImage`
 - `LandmarkGroup`
 - `LandmarkManager`

This also fixes copying for trimeshes in general. 

I snuck in some tests on the `FittingResult` as well.