Theme recommendations

Passing the recommended nodes to a theming function would give developers a lot more control over how this module's data is presented.

At the end of node_recommendation_recommendations(), do this instead of the node_view:

   return theme('node_recommendation_nodes', $recommendations);

and then move the node_view part to a function theme_node_recommendation_nodes($recommendations).

This would allow developers to present the recommendations as a list of titles, for example.