Put icons back in template parameter search

These disappeared when DecoratedOptionWidget was split
out of OptionWidget in I508c1555 in oojs-ui back in July,
and apparently no one noticed.

Make MWParameterResultWidget and MWMoreParameterResultWidget
inherit DecoratedOptionWidget instead of OptionWidget so
the icon config parameter is recognized again.

Change-Id: I08d8a0466c211a29eb62043131725073dece4eb5
Merge "Put icons back in template parameter search"