Add check whether group is empty in scala reduce operator

This fixes #434
Reenable ClosureCleaner and add new Test case for everything

Closure cleaner did not work before because the user code class loader
was not used when it was trying to load inner anonymous classes.

The new test checks whether the ClosureCleaner works together with the
user code class loader.

It also used the local distributed executor and remote executor.
removeField method in Record class
Adding comments to removeField and uncommenting its test method
create basic project structure
Initial Raw test impelementation of Hadoop Input Formats capability
Code restructure
Some refinements on the hadoop input format

This is a combination of commits:
* make hadoop-compat compatible to hadoop yarn and remove org.apache.hadoop code
* Extended usercode wrapper, fixed IF serialization
* introduce pluggable type converter
* make the converter interface more generic; (hopefully) improved fetching logic