[FIX] made arguments and methods in BSpline2d const (if possible)
[NOP] updated test with new method signatures
Merge pull request #1051 from aiche/fix/const-correctness-for-bspline2d

[FIX] made arguments and functions in BSpline2d const (if possible)
[FEATURE] improved purity computation
[FEATURE] adds puritystate struct to track current precursor and followup scan
[FIX] fixed some float compare warnings
[FEATURE,INTERNAL] added faster purity computation that works in a single linear scan
[INTERNAL] moved purity computation into separate method allowing computation on different spectra
[FIX,FEATRE] fixed computation of follow up scan and implemented purity computation based on Savitski et al. 2011

 * removed debug output
 * adapted test purity values, values where manually validated
[INTERNAL] code cleanup and some more documentation
[INTERNAL] improved handling of experiment end case
[INTERNAL,PARAM] purity interpolation can now be deactivated

 * fixed small bug in purity computation
[INTERNAL] added alternative implementation for purity computation
[INTERNAL] improved purity computation
[INTERNAL] replaced purity computation with new version
[TEST] added test with disabled purity interpolation
[NOP] uncrustify
[DOC] updates class doc of IsobaricChannelExtractor
escape percent sign to fix usage documentation
fix time resolution of seed initialization: was seconds, now microseconds