Give plugins the ability to party harder on the Preferences panel.

Custom date formats are now directly possible, as well as alterations to any name-value pair.

Altered the inputLabel() function signature slightly, in a largely backwards-compatible manner, to allow for atts other than just 'class' to be applied to the wrapped content.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5752 2fea6a4d-a838-0410-917b-93a53c48e9d2