Drop down action for toolbars containing BuildpathModifierActions.
The drop down action manages a list of actions that are displayed when invoking
the drop down.
Displays a set of available links to modify or adjust the project.
The links contain a short description about the consequences of
this action.
The content depends on the selection made on the project.
If selection changes, then the HintTextGroup will be
notified through the IPackageExplorerActionListener interface.