Overload #execute to allow call to ModelTree#setComponent

ModelTree#addComponent adds a new TreeItem, while #setComponent reuses
an existing TreeItem.
Progress in deserializing driver

Make sure the action menu is active, and display the name of the model.
Update methods for locating open ports in ModelTree

ModelTree#findOpenModelCells becomes #findOpenComponentCells. Applied
to no-arg version and overloaded version that accepts a TreeItem.
Deserialize components connected to driver component
Add new static member DataManager.DRIVER

It's used in several places in WMT to identify the id of the driver
port.
Add "link" style to CSS rules
Experimenting with styles for ComponentCell
Add "linked" components to ModelTree

The code works, but it's horrible. It needs to be refactored.
Can now deserialize a saved model