Bug 1165616 - XLS decision table screen does not show up if the xls file does not meet the XLS-DT requirements

(cherry picked from commit 2c63cf98a96321318b588a6568ff8535de25a22e)

Conflicts:
	drools-wb-screens/drools-wb-guided-dtree-editor/drools-wb-guided-dtree-editor-client/src/main/java/org/drools/workbench/screens/guided/dtree/client/widget/popups/ParserMessagesPopup.java