#134 Galago: Support #rm1 and #rm3 rather than just #rm

[John Foley]

Right now to get at RM1, you need to add the query parameter --expansionModel=org.lemurproject.galago.core.retrieval.prf.RelevanceModel1 and use #rm(), according to ExpansionModelFactory and RelevanceModelTraversal It would be nicer if RelevanceModelTraversal supported #rm1 and #rm3 as those are definitely built in, and only fell back to a full classpath if you implement something new. I like that #rm still defaults to RelevanceModel3.