Nest to nest matching implemented

An empty nest matches any nest.
Fixed a bug creating a widget from JSON

Was treating parts of widgets (e.g. a robot's actions) as a widget.
Nests in conditions no longer connected to original

Fixes #123.
Added support for robots manipulating nests

If a robot is trained to pick up a nest then it will do so even if the
nest is covered.

Also fixed a bug in paths to backside elements.

And removed obsolete code.
Getting the side of undefined now returns undefined
Added comments and removed commented out code
Removed obsolete code