Store boolean component parameters as true/false i.s.o. on/off

Apparently, boolean component parameters (represented by checkboxes in the UI) are stored as Strings of value "on" or "off" in the hst:parametervalues property of an hst:component. While HST abstracts that nicely for normal usage, these values are exposed transparently through the Page Model API.

For version 14 (since this is a non-BC change), either the values should be stored as "true' and "false", or the Page Model API should apply the same conversion as the rest of HST does.