Fixes Null marshaling in collection and List tests

- CollectionMarshaler was throwing exception when any item was null
while getting the approx DS type of the items in the collection. Fixed
this by proper null check.
- Removed ArbitraryDimensionArrayImport from IList parameters as by
default IList will be marshaled as arbitrary dimension array.
- ArbitraryDimensionArrayImport attribute is applied to item parameter
of AddItemToFront method, so that a collection can be added to the front
of the list.
- indices parameter of method List.RemoveItemAtIndex is changed to int[]
from object so that only integers are passed. VM will automatically
promote single object to a collection while calling this method.
Added a test case for list with null element
Before running an expression, clearing its associated warnings
Changed the migration of Compare nodes
Added input type casting for "List.Sublists"

To support non-integer (double) inputs
Marked test case as inconclusive

- Dynamo.Nodes.Formula
Merge pull request #1292 from ke-yu/fix_spurious_error

Before running an expression, clearing its associated warnings
Merge pull request #1293 from ellensi/ChocoButter-2Become1

Various fixes
Merge pull request #1290 from sharadkjaiswal/DataMarshaling

Fixes Null marshaling in collection and List tests
Form.ByLoftingCurveElements
Merge branch 'ChocoButter-2Become1' of https://github.com/DynamoDS/Dynamo into ChocoButter-2Become1
Get search tags for FunctionDescriptor, xml documentation, add to search dictionary
Ensure in Transaction when regenerating BoundingBox
MAGN-2305. Crash on attempting to get input identifier from empty list.
Merge branch 'ChocoButter-2Become1' of github.com:DynamoDS/Dynamo into ChocoButter-2Become1
Make abtract element implement IGraphicItem to thwart GraphicDataProvider property inspection.
Add CoreNodes reference for RevitNodes to get DSColor.
Add ProtoInterface reference to RevitNodesUI to resolve IGraphicItem reference.
TransactionManager.DoAssertInIdleThread - parameterize whether transaction manager should make this assertion, Turn off when running DynamoTestFramework
Merge branch 'ChocoButter-2Become1' of https://github.com/DynamoDS/Dynamo into ChocoButter-2Become1