Underground Planning

Game should incorporate and underground planning mode. This is so one can plan things beneath the "above" ground ghosts without running into collision issues. Currently, ghosts act as if they are real entities that can collide. Logistic vehicles path around them as if they were built.

While in underground planning mode, entities that can be buried like pipes are allowed to be extended below and into the soil/substrate where the cursor is currently placed. The planned underground entities should be visible when the soil around it has been dug out or prepared.

There should be a trencher/horizontal pipe coring machine like the excavator. The sole purpose of this unit is to lay casings along the planned underground paths. These casings are the housing of the underground transport entities. This is required to prevent accidental deletion of the built underground entities, which frequently occur due to misclicks. Finally, underground things can only be removed while in underground mode.