Allow multiple objects to have their parameters edited simultaneously

[Edgar Berdahl]

If the user selects N objects of the same type (where N>1) and double clicks on any one of the objects, then a window opens allowing the parameters of all of the objects to be changed at the same time. (Only fields that are all the same should be editable. Otherwise, fields should be grayed which are not the same for all of the selected objects.) (Some fields should always be grayed out in this case: the identifiers should not be all simultaneously editable, and neither should the starting and ending vertices.)

(If user double-clicks on objects and they are not all the same type of object, then just open the one that they double-clicked on. (e.g. it's not possible to edit parameters for a mass and a linear link at the same time))