Add validation tool for lisflood

[domeniconappo]

Users can run the tool to verify that

1. Input netCDF4 files (forcings) have the right metadata, variables naming, CF 1.7 compliant
2. mask map of the area is correct

[salampe]

Ideally, there should also be a check on each map for bogus values (e.g. negative precipitation, all maps have values where the mask map is "true", etc.)

[domeniconappo]

Related to
ec-jrc/lisflood-code#31