Use walker for legal, costs, maintenance reasons. Fix #3

[faerietree]

Foundation for such a big movable tower was too expensive and big.
Security was an issue (fence mandatory).
Static installation as a tower meant no other use possible.
Illegal because a tower is only permitted for radio transmission, energy harvest (e.g. wind).

Mobile walker fixes all these issues and reduces the amount of machines to maintain.
Blocks constructing prototype because there is a dependency chain. Order of construction:

1. walker
2. manipulator
3. fruit nut vegetable gardener

[faerietree]

Fix #3