The all new preview control

Background
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1. The preview bubble (and the little triangle below nodes) and all relevant codes are completely removed
2. The only place that makes use of ```InfoBubble``` now is the error/warning bubble on top of nodes (these are to be removed with later pull requests as they behave significantly different from preview control)
3. ```Dynamo.Nodes.Watch.Process``` method is made static so it can be used in ```PreviewControl```
4. ```Show/Hide All Preview``` menu item is now removed (need discussion on how this functionality can be repackaged with the new ```PreviewControl```
5. A new ```Canvas``` (named ```expansionBay```) has been added to the bottom ```NodeView.xaml``` to host the new ```PreviewControl``` (which is generated only on-demand)
6. The new ```PreviewControl``` has three main stages: ```Hidden```, ```Condensed``` and ```Expanded```.
7. The tree-view in an expanded ```PreviewControl``` is only created when user chooses to expand the preview, hovering over to the small preview icon will not unnecessarily create the heavier tree-view.
8. When the evaluator thread updates a ```NodeModel``` (i.e. setting its ```IsUpdated``` to ```true```), the corresponding property changed notification schedules an update on the UI thread (by going through ```Dispatcher.BeginInvoke```) instead of directly updating the contents of the ```PreviewControl```

Outstanding Issues
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1. We may still need a way to reintroduce the ```Show/Hide All Preview``` menu item. The fact that constructing tree views for each node on the canvas has significant overhead in every single way might not make this a very appealing thing to do.

2. ```NodeViewModel.IsPreviewInsetVisible``` property is now based on the name of the node to determine if the preview icon should be displayed for a given node. This needs to be turned into a virtual method that is implemented in relevant node types.

3. ```NodeModel.PrintExpression``` method is Scheme related and it still needs to be removed.