Add union operator in extractors and global schema printer
Add Union node in postpass extractors and Schema printer
Add new (naive) global schema generator

Still keep the old one around in case things don't pan out. The new one
just assigns output fields starting from 0, they are not globally unique
anymore.
Add BulkIteration support in scala

Unfortunately unions do not work in iterations but this problem also
occurs in an equivalent java implementation.
Bring code up-to-date with newest stratosphere-ozone