This changes should improve the situation with fires.
Also frequently requested mechanism of priorities is added.
- added priority system for drones
- maintenance start bonus increased from 4 to 5 (means first 5 buildings doesn't need maintenance)
- maintenance parameter now independent from electricity and depends only on workers count (workers can affect only as -40% maintenance building count) (means city didn't burn when no electricity period, and more stable when peoples is leaving city)