[Feature] ib spectra format export

 * IBSpectraFile can directly convert cXML to ibspectra format supported by isobar
 * includes test and documentation
 * as it is a pure csv based format it was not added separately to FileTypes
 * added conversion code to FileConverter
 * added corresponding topp tests
 * fixed minor issue in topp tests of MRMTransitionGroupPicker
 * unified add_test/ADD_TEST usage in src/test/topp/CMakeLists.txt