Added support for 'watched' robot steps

But no actions defined yet.
Improved debug_string

Updated when robot updated. Also removed redundant computation of
debug_string.
Removed an unneeded box debug_string
Backside widget problems resolved

It used to include open backsides (e.g. of the thought bubble contents).
Also is used in time critical code. So now is maintained
programmatically rather than computed by inspecting the children
elements.
Fixed loss of click handler

Frontsides were using JQuery .click() but then if removed and
re-attached the handler is lost. Using onclick instead fixes this.