Added release/retain semantics to KijiTable

 - removed AbstractKijiTable.
 - modified kiji-schema build to fail if resources are not closed in tests.
 - KijiTable.close() is deprecated.
 - HBaseKijiTable is final.
SCHEMA-228. FormattedKeys: allow nulls in hash calculation

Formatted Keys throw IndexOutOfBoundsException when null is present
in the components that must be hashed. Fix this so that hash(['aaa', null])
= hash(['aaa']).

Signed-off-by: Aaron Kimball <aaron@wibidata.com>