EXP-232.  Merge modeling in/outspec with flow API.

Update KijiInputSpec, KijiOutputSpec, KijiSingleColumnOutputSpec to more
closely match the argument lists for KijiInput and KijiOutput from
org.kiji.express.flow.

This change allows us to remove ExpressColumnRequest and
ExpressDataRequest.

This change depends on a pending change to the KijiExpress flow API that
absorbs the ExpressColumnFilter as a member of ColumnRequestInput.

As part of this change, move ExpressColumnFilter and the other Express
filters to org.kji.express.flow.

review: https://review.kiji.org/r/1284
issue: https://jira.kiji.org/EXP-232