Parser

Added an XML file parser. OpenPixi uses the parser when started through MainBatch with a file path argument. If no argument is provided the parser is not used and the program reverts to the defaults. This is also true for other exceptions.
It might happen that the file is only partially processed, in that case OpenPixi informs the user about it by printing an error message to the console. The program then continues execution with partially new and partially default parameters.