IDPosteriorErrorProbability fix

[FIX] IDPep: remove unused output files (output_name)
- naming of output parameters + hiding of redundant params in subsections
- gnuplot script now writes PDF instead of PS (better platform support)
- fixed some bugs which lead to SegFault when q-values are provided (from FDR upstream)
- avoid new() and use stack instead (there was a mem leak btw)
- fixed some potential segfaults (getMetaValue without metaValueExists)
- docu fixes
- code cleanup