Support for an inspector

[slisson]

The inspector in MPS is used to keep the main editor more readable, but also allow to edit the details if needed. This can also be a disadvantage. Some users don't like that they can't see the whole definition of the model and don't know when there is more hidden in the inspector.

A separate tool window for the inspector doesn't work so well in the browser. Maybe we can show a small icon that opens a popup with an editor. Then it's clear where more details are hidden, you can have multiple inspectors per node and you can have inspectors inside inspectors. It's more like an editable tooltip.