feat(Entity): expose Dictionary as part of the public API (#1118)

Closes #865

Author: alex-okrushko

modules/entity/src/index.ts

@@ -1,2 +1,2 @@
 export { createEntityAdapter } from './create_adapter';
-export { EntityState, EntityAdapter, Update } from './models';
+export { Dictionary, EntityState, EntityAdapter, Update } from './models';