Improve the Property.registerAggregate API

* So it only needs the aggregate property name and list of fields,
  instead of having a lot of duplication for unneeded flexibility.
Add back the Panel files by copying them from Mozart 1
Introduce the necessary properties to run the Panel

* The build is simple as this is a single functor.
* The "Problem Solving" tab is not working yet.
Sort aggregate properties by alphabetical order in Property.oz
Add needed properties for the Panel "Problem Solving" tab
Merge pull request #172 from eregon/panel

Bring back the Panel!