lake and urban fractions (sftlaf and sfturf)

[gnikulin]

there are 2 static variables defined in Tier2, both were archived so it should be very straightforward to postprocess them I hope

sfturf - Percentage of the Grid Cell Occupied by Urban Area
sftlaf - Percentage of the Grid Cell Occupied by Lake

We only need to wait a bit for updating cell_methods for sftlaf WCRP-CORDEX/data-request-table#58

[ljoakim]

Ok, keep me updated, and I'll update the hclim2cmor table and test-run the postprocess on the vars as soon as the referenced issue is fixed.

[gnikulin]

We need to wait with sftlaf and sfturf, these 2 variables are a bit more complex than other fractions WCRP-CORDEX/data-request-table#58