Bug 5698: Add date picker option to SQL Runtime Parameters

Bug 5698: Add date picker option to SQL Runtime Parameters

Adds a date picker for SQL reports with the 'date' authorised_value.  Updates help
documentation for this new feature, as well.

To test:
1.  Create a new report with two date parameters, using the syntax:
<<Label for this selection of date|date>>
2.  Run the report
3.  Select dates
4.  The SQL generated should format the dates properly in ISO, and keep track of which
date is which

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>