Import 4D MagnesWH3600 files to fiff …

- this is a WIP please don't merge. Despite it's almost ready some tests are pending.
- Early / generic feedback is welcome however.

Finally, we are there. Some info for the others:
The script resembles the solaris export_fiff program once available for Solaris workstations. Instead of the hierarchical binary data files it processes the header and ascii files produced by different MSI routines, namely 'export_data' which produces xxx.data (binary: time slices x channels) xxx.hdr and ascii header file, 'sensor_transformer' which writes the general device to head transform into x.transform, and 'dump_hs' wihch writes the digitization points into a x.hs. As a consequence of the ascii export the precision is about 4-5 decimals. The script allows to compensate for a sensor frame misalignment between the default mne MagnesWH3600 settings and some particular Magnes3600WH Systems. Also the default translation can be set.