myrialang: various fixes
myrialang: various fixes

* Switch from PositionReferences to indices in output JSON formats
* Rename MyriaEquiJoin to MyriaJoin.
  * But throw an error when a non-EquiJoin is given.
  * TODO write a rule that replaces that case with a CrossProduct and a Select
* Modify MyriaJoin to be a ProjectingJoin, add OneToOne rule for
  ProjectingJoin => MyriaJoin
* Enable the Join,Project => ProjectingJoin rule
* Remove dead code (PartitionBy and Broadcast). It's not producing valid
  code right now.. we probably need it, but let's do that later on
  demand.

Signed-off-by: Daniel Halperin <1a02732a15f637c31107256cbee5819e36aa7c67@cs.washington.edu>

uwescience/raco,uwescience/raco,uwescience/raco,uwescience/raco,uwescience/raco