Core functionality to integrate MS data in pre-defined mz-rt areas

[jorainer]

Expose the fillChromPeaks core functionality (or equivalent) to support integration of signals in pre-defined m/z-rt areas (e.g. from featureDefinitions).
See issue #232

[jorainer]

Specifically, the functions are (depending on the method used to detect the peaks):

• .getMSWPeakData
• .getChromPeakData_matchedFilter
• .getChromPeakData

Would simply need to implement a wrapper function and export that (something like integrateData that takes an OnDiskMSnExp, and mz and rt ranges).