Possibility to deactivate relativeElevation

[Supsa]

Hi,
This is just a suggestion to make cwatm more user-friendly.
When using modflow coupling for groundwater process, the relativeElevation map is not needed anymore. Nevertheless, CWatM still requires it to run (creashed otherwise). As it can be quite cumbersome to create such a map (even a dummy one), the possibility to deactivate the need for this map when using modflow would be very useful :)
Best,
Alexandre