Support for collection parameters on actions

[richardpawson]

In Naked Objects, we now support actions that take a collection as a parameter - principally for the purpose of 'multi-select' from a drop-down list. (Previously we supported them only for the specific purpose of collection-contributed actions).

It would be useful if RO 1.1. could support this idea. I'm not sure if this needs to be an optional capability or not. It should not be a breaking change anyway.