EXP-29. Add Implicits containing implicit conversions.

This commit adds repl.Implicits.scala, which contains implicit
conversions necessary for authoring Scalding flows. This will be
useful in providing a REPL environment for authoring pipelines to the
user.

Reviewed by: kiyan
EXP-33. Add a KijiPipe that allows for running a Cascading Pipe.

This commit adds KijiPipe, which contains machinery for running a
Cascading Pipe directly. This is to facilitate running jobs in the
REPL.

Reviewed by: robertchu