ICBC updates from IU

[taobrienlbl]

• add an ICBC reader for data from the NCAR RDA version of ERA5

The new reader dattyp is called RDAE5. In the input data directory, RDAE5 should contain a dss633.0 subdirectory that mirrors the directory structure of the RDA dataset. The directory should contain the t, z, q, u, and v data files for the desired days, e.g.:

> ls RDAE5/ds633.0/e5.oper.an.pl/197901/*1979010100_1979010123*
RDAE5/ds633.0/e5.oper.an.pl/197901/e5.oper.an.pl.128_129_z.ll025sc.1979010100_1979010123.nc
RDAE5/ds633.0/e5.oper.an.pl/197901/e5.oper.an.pl.128_130_t.ll025sc.1979010100_1979010123.nc
RDAE5/ds633.0/e5.oper.an.pl/197901/e5.oper.an.pl.128_131_u.ll025uv.1979010100_1979010123.nc
RDAE5/ds633.0/e5.oper.an.pl/197901/e5.oper.an.pl.128_132_v.ll025uv.1979010100_1979010123.nc
RDAE5/ds633.0/e5.oper.an.pl/197901/e5.oper.an.pl.128_133_q.ll025sc.1979010100_1979010123.nc

[taobrienlbl]

@graziano-giuliani - I'm still testing this, so I suggest not merging quite yet. Initial tests look good though.

Let me know if this would be something you would consider merging and, if so, any changes you would suggest - thanks!