EXP-131. Better programmatic API for building model definitions and environments

 - converts Avro records to Scala case classes up-front.
 - hide accessors exposing Avro records.
 - Renaming:
   - KVStore becomes AvroKVStore
   - KVStoreSpec becomes KVStore
   - FieldBinding becomes AvroFieldBinding
   - FieldBindingSpec becomes FieldBinding

issue: https://jira.kiji.org/browse/EXP-131
review: https://review.kiji.org/r/791
EXP-151. Stop bundling KijiSchema in the tarball.

This will use the KijiSchema jar from $KIJI_HOME/lib.
EXP-120. Implement a trait users can extend to make their own prepare phase.

issue: https://jira.kiji.org/browse/EXP-120
review: https://review.kiji.org/r/793
EXP-107. (P1) File moves for package reorganization.

This commit is the first step of this KijiExpress package
reorganization. Only file moves are performed.

Reviewed by: daisy
EXP-107. (P2) Place types in packages for package reorg.

This is the second part of this KijiExpress package reorganization. In
this commit, package declarations are changed to agree with the new
organization.

Reviewed by: daisy
EXP-107. (P3) Changes to imports for KijiExpress package reorg.

This commit is the third part of the KijiExpress package
reorganization. It modifies code, scripts, and the README to agree
with the new package structure.

Reviewed by: daisy
Break out modle env into many files