Add attributes for selection node. Move to Dynamo.Nodes namespace.

Conflicts:
	src/DSCoreNodesTests/NodeWithUITests.cs
	src/DSRevitNodesUI/DSSelection.cs
Bring selection node work from MultiAssemblyLoadBranch.
Add selection test entries to xml.
Initialize the collection for the multiple element selection node.

Conflicts:
	src/DynamoRevit/DynamoRevit.cs
Remove RevitData type and replace with DocumentManager.

Conflicts:
	src/DSRevitNodesTests/Interactivity/SelectionTests.cs
	src/DynamoTestFramework/DynamoTestFramework.cs
Remove dynRevitSettings.Revit.

Conflicts:
	src/DynamoRevit/DynamoRevit.cs
Remove dynRevitSettings.Doc and MainTransaction.
Remove unused RevitPersistenceManager project.

Conflicts:
	src/RevitPersistenceManager/Properties/AssemblyInfo.cs
Add DSDropDownSelection.
Add select all elements of type.
Add logic to gather all selected elements when building ast.
Mark constructor on DS face as internal to avoid name collisions.
Merge remote-tracking branch 'upstream/ChocoButter' into CheeseGrits