Blender Git Loki

Basic snapping support for dropping objects

Uses the same snapping logic as the placement plane from the Add Object
tool, which means it matches the plane that we already draw as a
preview.

This is quite primitive at this point - you can't change options for the
snapping like the up-axis or the snapping target - but it already feels
quite great.
Another limitation is that it uses the origin of the dropped object to
place it, the bounding box should give better results in practice. This
is something we can add.