Changes to FMRIB configuration from most recent UKB release

• Recategorise 20107 (to 10) and 6671 (to 50)
• vt{31}=[25000:25746 25754:25759 25761:25768 25781:25920 26500:27772]
• Coding 272 - NaN replace
• Coding 300 - NaN replace
• Coding 819 - NaN replace
• Double check against Steve's MATLAB categories (last located at /vols/Data/ukbiobank/FMRIB/ANALYSIS/DO_12/subproc_2_nIDP_groups.m)