Updated entity.fetch

Added if statement to throw an error if type === undefined. Previously, if no type was passed to createEntity(), the SDK would create an 'undefineds' collection.

Also, type if required for all crud operations, so it makes sense to enforce it in fetch.
Updated createEntity

Two updates:

- Updated the callback function to align with the the callback being returned by fetch(). Previously, only two params were being handled by the callback function but three were being passed by fetch().

- Updated the okToSave var to accept errorMsg === 'cannot fetch entity, no name specified'. This allows createEntity to succeed even if no 'name' property is passed to it. Previously, the fetch() call was blocking creation of entities that did not have a name specified.
Merge pull request #14 from amuramoto/patch-9

Updates to createEntity and entity.fetch