[Suggestion] Harvester Abilities (Douse, Prospect, Triangulate)

This will likely be an unpopular suggestion, but I think it is illogical to allow purchase of higher tiers of these abilities without first purchasing the lower level version. These abilities should have the additional requirement of having possession of earlier versions in order to unlock the right to purchase it. For example, I should not be able to purchase Prospect V until I have III and IV.

Not only does this make sense, but this will keep harvesters from having these abilities too early. (At level 21 miner, I should not be able to purchase and use prospect IV for grade 4 areas considering I don't even have Lay of the Land IV yet and that ability is lower level than Prospect IV.)