STIX_Package level handling does not work well when you remove the objects from the STIX_Package (ie. Object reuse)

[terrymacdonald]

When you remove a STIX Object from its STIX package, the Marking Structure does not move with it. This would cause issues while extracting objects from a received package as one would need to extract the Handling Guidelines and then attach them to each object.

We need to find a different solution. One potential solution is proposed below:

1. Remove Handling/Marking from STIX_Package Header
2. Remove the concept of XPath Controlled_Structure
3. Find a new home for Information Source, outside of Handling/Marking
4. Create Simple Marking, TLP, and TOU marking as either attributes to each object or as elements within each object

[terrymacdonald]

This issue is related to #377 and #379