Implemented MapReduce example
- Added Map and Reduce service which both take another service as an argument and verify and execute the result with the help of the other service
- Added ListValue machine value which contains a list of values. This is the first part for list representation for the lambda caluclus. The parser and compiler part is not implemented yet
- Fixed a bug where a machine value caused a stackoverflow when adding another case class (because the toString method was overriden with the prettyprinter, which matched with all case classes. A match error throw an exception with a message which printed out the value to be prettyprinted, however, this calls the toString method again which caused a stackoverflow)