SCHEMA-534. NPE thrown when fetching iterator from KijiRowData

 - Add preconditions to check for a data request.

issue: https://jira.kiji.org/browse/SCHEMA-534
review: https://review.kiji.org/r/1124
SCHEMA-553. HBaseKijiRowData.getReaderSchema() isn't compatible with layout 1.3

 - Deprecate KijiTableLayout.getCellStorage(KijiColumnName)
 - Deprecate KijiTableLayout.getSchema(KijiColumnName)
 - The prefered way becomes to use KijiTableLayout.getCellSpec(KijiColumName).
 - Improve CellSpec javadoc.
 - AvroSchemaResolver becomes an interface, SchemaTableAvroResolver implements it.
 - Lots of fixes in CellSpec wrt. to the new AVRO type.
 - Proper CellSpec initialization with layout-1.3.

issue: https://jira.kiji.org/browse/SCHEMA-553
review: https://review.kiji.org/r/1140
kdd