removing zeros in profile data caused by Thermo bug

Some Thermo QExactive profile data contain zero intensity data points that are clearly not part of the profile. The example below shows two peaks in profile mode. Data points are roughly 0.006 Th apart. Right after the 4th and 5th data point, the spectrum contains two zero-intensity data points (green +). They are clearly artefacts and not part of the profile.

This pull request removes these zeros in the SplineSpectrum constructor and thereby ensures correct interpolation of the profile data.

![thermobugzeros](https://cloud.githubusercontent.com/assets/6149805/4941281/6ac8f932-65e1-11e4-8725-54ca7fabcf9f.png)

The new const scaling_Thermo_bug = 1/50 defines "highly non-equidistant" in this context. Highly non-equidistant in combination with zero intensity happens only for these Thermo bugs. An ugly magic constant. But the clean-up should not depend crucially on the value (e.g. 1/20 is probably fine too). Do not know how else to get rid of these datapoints.