RESTWS should allow modules to add custom searches to existing resources

This is related to RESTWS-310. As described in that ticket, only one module can add a custom search to a resource (see Roger-Darius dialog 2012-11-27). This ticket seeks to remove that limitation.

Can't we do something with a custom annotation something like @SearchHandler(resource,name=null,[required params],[optional params])? The "name" parameter is one way to deal with searches with duplicate signatures, it would identify this search with a known parameter (e.g. search) having the name value. Example:

@SearchHandler(person,"FindMother",["q"],null) 
responds to 
GET .../person?q=whatever&search=FindMother 
as an alternative to 
@SearchHander(person,null,["FindMother"],null) 
responds to 
GET .../person?FindMother=whatever

We might also need to do something about the way searches can return paginated or unpaginated lists.