Merge from DynamoDS/Dynamo:master to Benglin/dynamo:Sitrus

NB! YouTrack is not available at the moment. Next after login page says "Maintenance is in progress. Authentication is temporarily unavailable. Please contact your server administrators." Used stubs for links to tasks. All tasks will be added as soon as service started work.

#### Purpose

In PR https://github.com/DynamoDS/Dynamo/pull/2143 was made split of `DynamoCore` to `DynamoCore` and `DynamoCoreWpf`. As result we have significant changes in sources. Because Dynamo Library UI project is based on changed code it is not mechanical code merge and conflicts resolution. Generally logic left the same but some parts were moved to new places, a bit reworked.

#### Modifications

Resolved merge conflicts and build was made successful!

In initial PR were introduced ViewModels for all classes which are used in tree of nodes. For example: we have new `BrowserRooElementViewModel`, `BrowserInternalElementViewModel`,... From my side `ClassInformation` was reworked to `ClassInformationViewModel`. Changed references to new ViewModels in`LibraryWrapPanel`, `LibraryTreeTemplateSelector`, `ClassObjectTemplateSelector`, other code in `xaml.cs` which operated with model classes before. Also were fixed all connected converters, their tests.

Views were moved to new project `DynamoCoreWpf`. XAML was changed to work with `BrowserItemviewModel.Model.[property name]`.

Returned missed during previous merge margins.

#### Additional references

Make solution as built successfully [YouTrack taskN]
Use ViewModels of tree nodes [YouTrack taskN]
Fix obvious bugs connected with merge [YouTrack taskN] 

During work on PR were found some place which needs further work. It is proposed to create a new PRs for them:
1. Rework `LibraryCustomization` class to remove reference on WPF specific library `PresentationCore`.
2. Make work with ViewModels in `LibrarySearchView` view & code.
3. Take care on `SearchModel` failing tests. They are failed before merge. I have noticed it now.

#### Reviewers

@Benglin, please, take a look.