EXP-85. packAvro now expects to pack Scala types, not Java types.

The method packAvro in KijiPipe is used to pack multiple Scalding
tuple fields into one AvroRecord. To do this, the values in the tuple
fields must be converted to instances of AvroValue (really AvroValue's
ancestors). Before this commit, KijiPipe used AvroUtil#wrapGenericAvro
to perform this conversion. This is incorrect, however, as
AvroUtil#wrapGenericAvro expects Java types as input, but the tuple
field values to be packed should be Scala types. This commit changes
packAvro to use AvroUtil#scalaToGenericAvro instead, which expects
Scala types to convert to AvroValues.

Reviewed by: juliet
KIJIMR-205. KijiTableKeyValueStore should be keyed on row key components.

This commit updates kiji-express to be compatible with KIJIMR-205,
which changes how KijiTableKeyValueStore is keyed.

Reviewed by: juliet
EXP-88. Makes KijiSlice's apply() method package-private.

This commit modifies the access permissions of the apply() method
in KijiSlice from public (default) to package-private.

Reviewed by: robertchu
Avro defs of filters
Adds supports in data request
Add case classes for column filters
All tests passing,