[FIX] typeof null actually === 'object'

Fixed an issue where calling `isValue` with null would throw a
`TypeError` (Cannot read property then of null)
Add a store.normalize() method to make it easy to normalize record data for store.push()
Throw and error if a user attempts to add a `data` property to a subclass of DS.Model
Moved several normalize helper methods to the JSONSerializer
- Move `normalizeAttributes` to the `JSONSerializer` (mirrors `serializeAttributes`)
- Move `normalizeRelationships` to the `JSONSerializer`
- Move `normalizePayload` to the `JSONSerializer`
Added id and requestType back to extract* hooks

id and requestType parameters went missing in when removing aliasMethod. See commit dd964d2b7fe87ef7368336bd401c40834950f736 :
https://github.com/emberjs/data/commit/dd964d2b7fe87ef7368336bd401c40834950f736
Added a failing test for #2088.

This test ensures the serializer does not confuse a new record
returned in response to a delete with the original record when both
records are of the same type.
Coalesce find requests, add support for preloading data

This PR brings following improvements/changes:

1. Find calls from the same runloop will be coalesced into findMany
requests if the adapter has a findMany method
2. Adds a groupRecordsForFindMany hook on the adapter that allows you
to decide how to coalesce the record requests. This will enable fixing
of bugs such as #651, by segmenting on the number of records
3. Allows users to preset attributes and relationships on a model when
doing a find call. For relationships you can either pass in a record or
an id
4. Gives rudimentary support for nested urls, by passing in the record
object to the buildUrl method
5. Removes the owner being passed to findMany becuase it can be looked
up on the original record
6. Adds couple special cased SSOT features that were needed for
buildUrl/removal of owner property to be viable

This PR lays the groundwork for:
1. Adding support for reloading hasManys
2. Making nice sugar for nestedUrls in the RestAdater