SCHEMA-793. Implement AsyncKijiResult.

Implemented AsyncKijiResult, AsyncPagedKijiResult, AsyncMaterializedKijiResult,
AsyncKijiResultScanner, AsyncDataRequestAdapter, and associated tests.

issue: https://jira.kiji.org/browse/SCHEMA-793
Looks good overall.  I didn't go line-by-line because it looks like a copy of the HBase version.  If not let me know and I can go over in more detail.