SCHEMA-795. Design Async API.

Design an asynchronous API and create interfaces for the API.

issue: https://jira.kiji.org/browse/SCHEMA-795
Please remove `deleteFamily` methods and replace them with just two methods:

`deleteColumn(EntityId, KijiColumnName)`
and
`deleteColumn(EntityId, KijiColumnName, long)`

The family deletion case will be handled by passing an unqualified KCN to it.