PotentialNamespace should be in LayerFeature instead of Feature struct. Feature extractors were updated to return LayerFeature instead of Feature.
Feature's source feature string is directly stored in the database instead of having the parent pointer to simplify the database.
1. Featurefmt testing code is moved to featurefmttest package. 2. Featurefmt now can be tested against a csv file, which contains the expected package information result.