Provide observational data for multiple normal periods

[cmahony]

currently, we only have 1961-1990 and 2001-2020. ideally, we would have the option of other 30-year, 20-year, and 10-year periods. @cmahony will create the anomaly surfaces (north america) from CRU (temperature) and GPCC (precipitation).

[cmahony]

towards this goal, i wrote a script to calculate anomaly surfaces for north america. TransferAnomalies_calculate.R
it calculates anomalies for 10, 20, and 30 year periods starting in 1951, relative to a 1981-2010 reference period. this is in prep for when we have a composite climatology for 1981-2010.
I output the surfaces in a folder in devl called TransferAnomalies.

[cmahony]

i created a set of anomaly surfaces relative to 1961-1990 and moved all anomaly surfaces to object storage (\objectstore2.nrs.bcgov\ffec\TransferAnomalies) (these anomalies are using the CRU TS v4.05 for temperature and GPCC v2020 for precipitation).

[cmahony]

see related issue #303

[cmahony]

wait for aseem to build the new CRU-ERA5 hybrid time series.