[FIX] fixes random fails of MSSim_test

MSSim_test was run with multiple threads if OpenMP was available leading to random changes in the feature order and intensities. While this was captured in most of the tests it also led to minor changes in the number of selected precursors. This pull request sets the number of threads to 1 in the MSSim_test to avoid this problem.

Additionally, 

 * some `old-style-cast` warnings were fixed
 * `StringUtils.h` was added to `sources.cmake`
 * fixes some formatting issues in the travis-ci build names