Suppressed internally used Revit classes by marking them internal

This submission is to hide internally (non user-facing) used Dynamo classes from the UI. This addresses class name collisions between some user facing classes and internal classes having the same name as well as prevents them from showing up in code completion.

@sharadkjaiswal please review.
If the class or method is internal then we don't need to put IsVisibleInDynamoLibrary attribute. 
Can we have a small utility to dump the contents in library, and compare that with before and after these changes?