Update error messages from push and update

Error messages now include model type for ease of debugging
Add a base fiddle for mocked data requests with Ember Data
Removed unused resolver from ManyArray.fetch
Do not cache model factories on meta, or on other model CPs

Relationships are hard. Ember-Data has been storing data about a
relationship on the meta value for that CP. CPs hang around though, and
as a result that data on the meta becomes a cache. For some details
about a relationship, this is fine.

If User has many Posts, and you use User via a container, it would cache
a reference to the Post factory. But if you then destroy that container,
the reference to Post still exists in the CP meta. Furthermore, if you
create a new container and use User and Post via that new container,
the cache factory value for Post will be that of the old container and
not the new container.

This only is a problem if you expect to have Post be a different factory
in each container. In ember-cli, MODEL_FACTORY_INJECTIONS are enabled.
This means all factories are extended before being returned by the
container. So every time you have a new container, you have a new
factory (though it looks and behaves the same).

This change gets rid of that cache on meta. Instead it creates a
function that accepts the store and meta, and returns the relationship
object expected throughout Ember-Data. Two alternatives were considered:

  1. Always check against typeKey instead of instanceof, but this felt
like a dodge of the real problem and would leave the issue for others to
find, or
  2. Create a new first-class relationship object, but this would
be a far more invasive change, and would impact much of the codebase
that the current relationship object has already leaked through.

Additionally, the types were being cached on model class-level CPs. For
this patch, those have simply been marked cacheable(false). A later
patch should refactor the CPs out of the way, or at least re-write their
consumers to expect a relationship object without the factory itself
already fetched.
Makes sure extractArray is normalizing each record in the array instead of trying to normalize the whole payload as an object.

This was causing `applyTransforms` to do the transforms in properties of the array instead.
Merge pull request #1953 from bmac/fix-extract-array-miguel

Makes sure extractArray is normalizing each record in the array instead ...
Use keyForRelationship in JSONSerializer's serializeHasMany method

- serializeBelongsTo uses the same already
Merge pull request #1954 from emberjs/JSONSerializerKeyForHasMany

Use keyForRelationship in JSONSerializer's serializeHasMany method
[BUGFIX] store.fetchMany should always return a promise.
Merge pull request #1955 from emberjs/fetchManyAlwaysReturnsAPromise

[BUGFIX] store.fetchMany should always return a promise.
Merge pull request #1942 from duereg/master

Removed unused resolver from ManyArray.fetch
Merge pull request #1941 from mehulkar/base-fiddle

Add a base fiddle for mocked data requests with Ember Data
Add package.json to built gem

`Ember::Data::VERSION` is defined by `package.json` since 7d7ccfa44.
Without thi file, ember-data-source couldn't resolve own version.
Merge pull request #1871 from duereg/patch-1

Update error messages from push and update
Merge pull request #1956 from tricknotes/fix-gem-version

Add package.json to built gem
Update README
Merge pull request #1952 from mixonic/meta-cannot-cache-factories

Do not cache model factories on meta, or on other model CPs
Do not presume returned data arrays support .pushObjects

Returned data will cannot be assumed to be an Ember array object. A test
should not pass in an Ember array as API response data.