[Directory] Avoid tree collapse when expanding node in Create

Use updateMonitoredGUI (instead of explicitly interacting with the node) to trigger updating of a tree node when expanding. This addresses an issue (nasa/mct#106) where Create object causes the tree to collapse. The Create action automatically expands a collapsed node to show the new object, but the addition of the new object also causes the parent to be marked stale, triggering updateMonitoredGUI. If these events are resolved out-of-order the collapse occurs (this is JTree's fallback behavior when it has insufficient information to process a model change)

The node's updateMonitoredGUI has a fair amount of code to ensure that the tree's model is appropriately notified of changes; invoking this from the expand event causes the issue to disappear.

 Wrote or re-wrote unit tests (Y/N): N
 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: Browse 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

No unit tests included. Issue is timing-dependent, no new code paths introduced.