Editing variable nodes in the tree simplifier fails if the variable symbol does not contain any variable names

[bburlacu]

The insert new node and edit node dialog within the tree simplifier are not aware of the problem data, therefore the list of available variables is obtained from the symbol itself. But in some situations (perhaps with hand-crafted symbolic models) the symbol does not contain the allowed variables therefore crashing the dialogs.

[bburlacu]

r14432: Offer the user the option to provide the variable name when the symbol does not contain a list of available variable names. In this case the combo box is replaced by a text box.

[bburlacu]

r14494: Extend tree validity test in the InteractiveSymbolicDataAnalysisSolutionSimplifierView to test if all the variable names in the tree are contained in the solution problem data.

[mkommend]

Reviewed r14432 and r14494.

Please add the current variable name in the textbox when the dialog is opened, instead of using string.Empty in the textbox.

[bburlacu]

r14706: Set default variable value in the change node edit dialog text box.

[mkommend]

r14802: Merged r14432, r14494, r14706 into stable.