[Create] Fix layout for create dialog, nasa/mct#161

Reduces space consumed by create/cancel buttons in
object creation wizard, and adds padding (by way of
an empty border) around the dialog to match that
seen in UE specs for dialogs (see MCT-2788 on
private issue tracker for example.)

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: Code review by pull request
 Describe potential impact on other areas of the code: Create dialogs
 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
 Did you modify any pom.xml file? If yes, did you thoroughly document your changes and reasons? N

No unit tests for this change (it is aesthetic)