Add new DynamoSlider class.
Moved DynamoSlider to CoreNodesUI.
Move serialization shared logic into base class.
Hand-pick changes to slider classes and base class.
Remove dead IBlockingModel interface.
Fix two tests which referenced old Dynamo slider class.
Remove the old DynamoSlider class.
Remove two dead event handlers.
Rename to Number Slider and add search terms.
Rename double slider and add search terms.
Remove WindowsBase dependency.

Threading namespace is no longer needed. Remove WindowsBase reference
and cleanup unused using statements in several locations.
Visual tweaks to expander and slider.
minor code restructuring
Test commit of uncontroversial changes to PreferenceSettings.cs
Ripple changes from rename DYNAMO_TEST_PATH -> DynamoTestPath
Merge pull request #3440 from DynamoDS/MountainEater

Preference Settings minor changes
Redundant qualifier removal in UndoRedoRecorder
Merge pull request #3441 from DynamoDS/MountainEater

Redundant qualifier removal in UndoRedoRecorder
Whitespace change to IPreferences.cs
Safe changes to ModelBase.cs
Merge pull request #3442 from DynamoDS/MountainEater

More minor changes