Add fuel tank and solid fuel support

No idea what "tank.level" was supposed to be, changed to capacity.

Always treat fuel as a tank, if we're solid-fueled then just pretend
it's a tank of size 64.

If a tank empties out and goes away, we still need to update it to
indicate that. This needs some testing.
Add important boiler status output

This will all get prettied up in the future, but for now, just print out
data so we can see if it's working.