get_metadata_val is splitted into 3 functions:
  get_metadata_val_classic -- original code of get_metadata_val
  get_metadata_val_header -- retrive metadata from nifti
  get_metadata_val_bids -- retrive metadata from bidsified json

The get_metadata_val checks if recieved structure contains
'acqpar' and based on it colls one of 3 functions

Added:

 - isDWI from filename suffix
 - AllDiffusionDirections from bvec file
 - AllDiffusionValues from bval file

In order to get this info, added a new field to meta structure:
'filename' containing the path to data file.

bval and bvec are retrieved by changing extension

When possible the metadata structure is loaded and passed to the 'classic' or 'BIDS' get_metadata_val subfunctions.

Since there should not be any direct call to this function with a filename, one can remove the reloading of the mstruct based on a filename.

This is NOT in BIDS spaces but could be useful for some old data. It's only an added features and does not break back compatibility.

After looking for the 'TotalReadoutTime' field, one need to load the associated value then proceed.

…liy-get-metadata-bids

Synchronising master branches

Slightly more informative error message if number of images and angles don't match; using assert syntax (rather than "if X, then error"); replaced a couple of "echo1", "echo2" in comments that had been missed; matched indexing of P to the rest of the code (avoiding potential errors if P given as 1xN array); no longer need to account for possibility of "extra" elements in the P array (because of explicit assert statement).

… structs instead of char arrays. Added extra assert statement to check image pairs provided.

Added reordering of B1 maps following their fa