Add Smart Mulch feature

[Terraeris]

This adds a new toggle to the Simple Auto Farmer script.
When enabled, it will apply Rich mulch to plots that are about to be harvested, as to maximise Rich Mulch usage and increase yield.
Only applies when Auto Harvest or Auto Replant are active, and toggles Auto Mulch off (and vice versa, like with Auto Harvest/Plant and Auto Replant).

This will also close #278 as it satisfies the request.

This could be improved so that it applies boost mulch until the plant is ripe (then applies Rich mulch when harvesting and shovelling before and after applying the rich mulch), but that was out of the scope of what I was planning to achieve for now.