Document new parameters on gallery macro

There are a couple of sorting related parameters now available in the gallery macro to resolve CONF-4778.

The images section of the notation guide needs to be updated to explain them.

The added example is shown here -
https://svn.atlassian.com/privateeye/browse/private/atlassian/confluence/trunk/conf-webapp/src/main/webapp/renderer/notationhelp.vm?r1=42444&r2=46239

And the added explanation is shown here -
https://svn.atlassian.com/privateeye/browse/private/atlassian/confluence/trunk/confluence/src/etc/java/com/atlassian/confluence/core/ConfluenceActionSupport.properties?r1=45845&r2=46239