Fixes some RPD bugs

Fixes pipe painting not working
Fixes 4-way manifolds and disposals chutes displaying broken icons
Fixes the lack of Sort Junctions from the RPD
Fixes #6627
Fixes drones being unable to use the RPD
Merge pull request #6630 from tkdrg/rpdcolor

Tested, appears to be functioning as advertised. Cue drones making absurd disposal rides.