[Platform] Add Move, Copy options for Drag-and-Drop

In addition to current "Add Manifestation" linking behavior, add options to Copy or Move when dragging and dropping in the directory area. This supports nasa/mct#179

Change includes:
* Separate out internal details of handling the changes to the object model to a separate class; the directory area now simply prepares the appropriate request.
* Allow contained views to identify their container (specifically, allow node views in the tree to identify their parent node); this supports the ability to Move, as knowledge is needed about the source of the Move.
* Pop up a dialog showing available composition options (among Move/Link/Copy), if more than one such option is available. (See nasa/mct#179)

```
 Wrote or re-wrote unit tests (Y/N): Y
 Ran entire suite of unit tests successfully (Y/N): Y
 Verified bug fix with the described replication steps or verified the implementation meets the requirement cited (Y/N): Y
 Code coverage requirements satisfied (new code=80%, changed code=at least as high as existing) (Y/N): Y
 Code review date and attendees: Self-review by pull request
 Describe potential impact on other areas of the code: Drag-and-drop in the directory area
 Describe any test prerequisites for this fix (e.g., restart the database): N/A
 For bugs marked "Regression - Yes", describe the cause of the regression: N/A
 Did you modify any pom.xml file? If yes, did you thoroughly document your changes and reasons? N
```