Fix bruker spect sf

Created by: jtrebosc

Reference frequencies when importing from Bruker was not correctly handled. This pull request fixes the way SF is calculated in processed data and in acquisition data importations. For acquisition import, one problem is that reference frequency (SF) is stored in processing parameters in pdata subfolder. There can exist several processed datasets with different SF parameters. Some processed data can be projections or slices of specific dimension. The new import search across all pdata folders for processed parameter files of the same dimensionality as acquisition parameters as defined in ParMODE. If several sets of ref frequencies are found it uses the set of lowest procno number and displays alternate sets in metadata.

I'm waiting for possible comments before accepting the pull request. Best, Julien