Added matlab scripts to process UK Met Office observations

[arango]

I updated the matlab/4dvar repository and added two new scripts to process the UK Met Office datasets:

• 4dvar/d_ts_metoffice.m: Driver template to extract hydrographic potential temperature and salinity profile data from the UK Met Office observation datasets.

• 4dvar/load_ts_metoffice.m: Extracts potential temperature and salinity profiles from the UK Met Office, quality controlled, EN3 observation datasets. The data are available from 1950 to the present and include XBT, CTD, buoys, thermistor chain, and ARGO floats.

Various scripts were updated to allow concatenation of vectors consistent with the singleton dimension. This generalize the use of 4D-Var observation processing scripts.

The utility/nc_read.m script was modified to allow processing string arrays with _FillValue. This is need to process the UK Met Office datasets.

Corrected crucial bug in 4dvar/obs_depth.m when removing outliers in the observation structure.