Make ActiveModel a dependency and fully implement its interface

Change-Id: Ie6834387c154165f2f3a853d2b9a59072516b0ef
Reviewed-on: http://review.couchbase.org/29623
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>