localize all non-infrastructure endpoints
properly save sensor registry on shutdown
replace sensor registry and cache with a more generic device tree
display sensors without known value as disabled and don't display old sensors

for time being, a sensor is considered "old" if it hasn't sent a value
for at least one hour. if the sensor does send a value after that, it
will be displayed again.
unregister devicetree events on socket disconnect

otherwise we might leak memory, and we better not do that
add "forget device" button
Merge branch 'development' into pb-hexanode
periodically enumerate devices on the network
propagate all endpoint events to clients
add actors page to template
modularize endpoint visualizations

so far, only gauges are supported. coming up: buttons for boolean
actors!
add boolean actors

they're ugly as day right now, but we're getting somewhere at least
Merge branch 'pb-hexanode' into development