Add a command line interface to NESTML.

[DimitriPlotnikov]

NESTML has now following options when it is invoked from a terminal.

usage: The NESTML command line tool can be used as 'java -jar nestml.jar
           <options> path_to_models'. Valid options are listed below:
 -d,--dry-run             Use this option to execute the model analysis
                          only.
 -e,--enable_tracing      Enables tracing of templates which were used to
                          generate C++ code. It can be used for debugging
                          purporses.
 -h,--help                Prints this message.
 -j,--json_log <arg>      Defines the name of the file where the model log
                          will be stored in JSON format.
 -m,--module_name <arg>   Defines the name of nest module which is
                          generated with neuron models. Under thisname the
                          module can be installed in SLI/PyNEST.
 -t,--target <arg>        Defines the path where generated artifacts are
                          stored. The only argument determines the folder
                          where the generated code is stored. E.g.
                          --target ~/my_path