handle MDH_SLICE_ACCEL_REFSCAN, RawDataCorrectionFactors, and trajectory data sorted in sSYNC

[sbaete]

Hope to contribute my local changes to your mapVBVD.

• extract MDH_SLICE_ACCEL_REFSCAN-lines as a separate slicerefscan-object, similar to refscan. These slicerefscans are used e.g. in the product TSE when running SMS which forces TSE/Separate-reference lines. If these slicerefscan-lines are not separated, they are be added to the main image-object.
• code to read the RawDataCorrectionFactors
• extract and make ulTimeStamp, ixToRaw and ixToTarget available in the twix-map-obj
• ability to extract trajectory information stored in sSYNC-objects
• added check to see if data is sSYNC, in which case the header size is different (this.fReadInfo.complex)
• in read_twix_hdr, extend parse_xprot to extract more data and stor in the hdr-structure. Adding three helper functions extract_brace_string, find_next_tag, and safe_fieldname, the first two derived from parse_xprot.m from E. Auerbach, CMRR, 2013
• option to only read the header and skip indexing the rest of the datafile

Thank you for making mapVBVD and sharing it with everyone, it has been very helpful over the years.