Change in how Metatag loads entity info

Prior to v7.x-1.5 Metatag would load all entity information at once. This lead to conflicts with some modules, e.g. commerce_coupon which then would do its own entity_load(), which lead to metatag_entity_load() executing & caching its results before Metatag had finished identifying which entities were enabled for use with Metatag. With v7.x-1.5 Metatag will instead only verify each entity type when it's individually requested, which avoids problems with prematurely caching incorrect data but makes it slightly slower to check a number of entity types sequentially.