[ADD] implemented add and remove functions to manipulate lists
[ADD] use choices option of argparse
[FIX] interprete add/remove values as json
[FIX] catch json exceptions
[ADD] accept "self"-keyword in set operations;
[DOC] docstring for add and remove functions
[FIX] show error message if srvid can not be build;
[FIX] corrected return-code-handling;
[ADD] allow self-keyword in register and delete function;
Merge pull request #19 from aboutyou/develop

accept self-keyword everywhere and implemented add/remove functions