Don't destroy user-specified DataSourceCollection.

When Viewer is destroyed, it should only destroy its DataSourceCollection
if it created it.  A user-supplied DataSourceCollection is owned by the
user.
Merge pull request #1863 from AnalyticalGraphicsInc/viewerDeletesDataSourceCollection

Viewer should not destroy user-specified DataSourceCollection
Merge remote-tracking branch 'origin/master' into private