Refactor LayoutCapsule into separate interface.

Can be used now by HBaseKijiTable and CassandraKijiTable.

Also create many of the classes necessary for accessing a KijiTable
backed by Cassandra (no implementations ready yet, just scaffolding).
Very early C* put and get commands work in one test case.

This is a fun milestone.  TestCassandraCreateKijiTable has an example of
putting a few data values into a table and then reading them back.