Add helper to CurrentDate for NXQL query

As of today, using the CurrentDate wrapper in NXQL queries is not completely straightforward and error prone.

Select * From Document Where dc:created < DATE '@{CurrentDate.format("yyyy-mm-dd")}'

or

Select * From Document Where dc:created < TIMESTAMP '@{CurrentDate.format("what is the correct format ?")}'

Would be a lot easier and faster if there were helpers so that you don't need to ask yourself what is the correct format.