Add filterpresets allowing json filters to be defined in templates

the <parameter name="datasource"> element in tgrid templates now
can contain a filterPresets child which applies the containing json filter
to the grid. Example:
 	<parameter name="filterPresets">
        <![CDATA[
            {"AND":[{"field":"host_name","label":"Host","operator":"contain","value":"localhost10"}]}
        ]]>
	</parameter>

fixes #4483