Minor fix for displayed estimates.
[FLINK-935] Fix compiler logic that pushed work out of the iteration loop.
Made FieldSet and FieldList immutable collections to prevent bugs to to side effect mutations
Made LocalProperties Immutable (avoid side effect mutation bugs)
Change several Iterators to Iterables in the compiler (simpler code)
[FLINK-935] (continued) Correct feedback property check for iterative algorithms.