also make shower tray turn off taps above it, if any
minor tweak to particles function to add Y velocity
added more detailed collision boxes to the sinks to accommodate particles
when placing, code will try to determine if the bannister should be
left- or right-sided. Defaults to left-sided; hold shift while placing
to force right-sided.
create it by placing two twins of the same color side by side, left first
also moved the bed extension functions into handlers/expansion.lua,
renamed them, and made a few other minor tweaks to that file accordingly.
