PDI-11394 - Empty database browser dialog appears after unsuccessful connect to DB

Fix behaviour with empty database explorer shown for not success
connections.
Introduced new interface IUiActionStatus and enum UiPostActionStatus to
have ability to read status for reflective calls with exceptions
suppression.

Since Xul is not widely implemented and behavior described in bug is a
private case, this fix only applied for XulDatabaseExplorerController
and
XulDatabaseExplorerDialog classes for 'discover table' ui calls.

junits added into /test folder.