Refactor OrcStorageManager
Move mapping of symbol to channel to execution layer

This was incorrectly being done in the planning layer, which
only deals with logical entities.
Remove CodeCache workaround

This is no longer an issue in Java 8
Switch to Docker based Travis builds

This should give us 4GB of memory instead of 3GB and also more CPU
resources
Fix comparison of types in analysis of UNION
Fix TpchColumnHandle.equals() to compare types correctly
Fix comparison of types in AggregationCompiler
Add CLI program to benchmark a Presto cluster