Update test_helper and gemspec
Add models for persistence tests

Copied over all persistence models as of #1471f533ea and included
DynamicPersistence
Add tests for DynamicPersistence
Add DynamicPersistence functionality
Update model_persistence_test.rb to latest version from Tire
Change model_persistence_test for DynamicPersistence compatibility

Changed this test because DynamicPersistence accepts elasticsearch
meta_attributes as attribute_names on creation.
Merge branches 'dynamic-attribs' and 'master'