spline interpolation of MS1 spectra

Raw profile data provide intensities for a fixed set of m/z values. For some algorithm reliable intensities at arbitrary m/z are important. The maximum of the raw data of a peak and the maximum of its spline interpolation can differ significantly.

SplineSpectrum is a class for the fast interpolation of MS1 spectra. Raw spectra can contain data points of zero intensity with two neighbouring zeros. Removing such (useless) data points can reduce their number by up to 30%.

![splineinterpolation](https://cloud.githubusercontent.com/assets/6149805/2687840/92f6bf48-c271-11e3-9146-183e039f1fab.png)