renamed R2RMLExporter to SML2R2RMLConverter
also renaming and adaption due to now static converter

- since I made the SML-to-R2RML converter static (prvious commit) the
  initialization in the Run class was removed
- adjusted conversion call due to renamed the SML-to-R2RML converter class
added exmaple R2RML mappings
included Sherif's code for R2RML-to-SML conversion

- took Sherif's code and adapted the class name and main call method
  names to fit with the SML-to-R2RML converter
- also copied all helper classes and made them work
- sadly, the converter seems to be not complete and does not extract the
  predicate and object maps