Support changing of constants and variable weights in the simplifier for symbolic data analysis models

[bburlacu]

The SymbolicDataAnalysisExpressionTreeSimplifier should offer users the possibility of interactively changing constant values or variable weights.

Additionally, the tree model in the simplifier view should support the following operations:

• inserting an intermediate symbol between two nodes (ideally by selection or drag&drop from the available grammar)
• removing nodes/sub-trees (removing intermediate symbols or whole branches)
• "moving" nodes/sub-trees (manual simplification/collapsing or just some kind of copy/paste operation)

[bburlacu]

r7361: Updated project references, added build and solution files.

[bburlacu]

r7388: Added a new context option for leaf nodes (ConstantTreeNode or VariableTreeNode) to change the value or variable weight respectively.

• Added new dialog: SymbolicExpressionTreeNodeChangeValueDialog
• Added new SymbolicExpressionTreeNodeChanged event and handler
• Changed the double click behavior to account for node value/weight changes

Overall the behavior has been slightly changed: if a node was folded(replaced by a ConstantTreeNode), then it is possible to change its value via the context menu. For all changed nodes the original value is kept in a dictionary, so the first double click will restore it. After that, a second double click will unfold the node.

[bburlacu]

r7411: Improved ValueChangeDialog and overall behavior. Implemented pruning operation on background thread. TODO: Test, improve. This is a work-in-progress.

[bburlacu]

r7422: The simplifier view now uses a clone of the current model, on which the actual simplification or tree pruning is applied. This fixes a crash when the user clicks on the Symbolic Regression Model while the background thread is pruning the tree (because it was trying to display the tree while it was being changed). Also took out the display part from the CalculateReplacementNodesAndNodeImpacts method and put it in a separate method.