SCHEMA-793. Implement AsyncKijiResult.

Implemented AsyncKijiResult, AsyncPagedKijiResult, AsyncMaterializedKijiResult,
AsyncKijiResultScanner, AsyncDataRequestAdapter, and associated tests.

issue: https://jira.kiji.org/browse/SCHEMA-793
As in create a whole `Factory` subclass or just have a public static method `create()`?