Enable graceful handling of Searchlight::Search::searches sans DB

Enable users to gracefully handle the eager-loading of a Searchlight::Search class with a call to ::searches prior to DB creation (e.g. during a call to `rake assets:precompile`) by monkey-patching Searchlight::Search::model_has_db_attribute?
Merge pull request #15 from mnarayan01/master

Gracefully handle eager-loading of a Search prior to DB creation