TMDM-7768: "xsd:duration type doesn't work"

Maps xsd:duration to java.lang.String (in turn mapped to varchar in database).
Updates unit test accordingly.
(https://jira.talendforge.org/browse/TMDM-7768)
TMDM-7749: "Error message when welcome page refreshes due to a statistics problem"

Don't throw exception if a query on storage failed due to a closed storage (adapt all statistics services for this).
(https://jira.talendforge.org/browse/TMDM-7749)