added Friends model for testing. copied friends.csv from test.csv.
should use friends.csv in other tests.
initial test on Model and Friends class.
fixed to accept both Property{Csv|}.
Entity can be accessed as an array.
after testing Model, decided that Model only takes care of arrays, not entity object.
moved entity related stuff in Model to EntityManager.
Model's update to accept the same as persistence's update.
added test for Rules and Selectors.
added get{Rule|Selector} methods for presentation.