Stabilizing InfoBubble

Background
---
This pull request mainly involves the stabilizing of info bubble (preview, error etc.) by refactoring all the UI value changing operations to View instead of performing them in ViewModel.
With this pull request, InfoBubble is still not completely thread safe and has more room for stabilizing. One such case is the workaround that has been put in place. Currently, InfoBubble UI value changes are dispatched back to the UI Thread if it happened to be called from the background evaluation thread. These UI value changes should be restructured into WPF data binding which is thread safe.

Changes in this pull
---
1. Removed Opacity from InfoBubbleViewModel (Deprecated)
2. Re-factored InfoBubble so that UI changes are performed in View instead of ViewModel
3. Shifted thread dispatcher from NodeModel to InfoBubbleView
4. Fixed fading out which is not working

Recommended future changes
---
Restructure info bubble to use data binding to make it thread safe.