Heat update

[exinfinitum]

• Rename all occurrences of ship "counter" to "heat" and remove all occurrences of "counter" being referred to as "energy" including weapons that "consume" energy, or HUD display showing it as "energy"
• Add field that allows all devices to increment or decrement heat each tick, both while enabled and disabled (for now) - maybe some other functions for things like weapons and shields like e.g. shields generating heat while taking damage
• Add field that allows all armours to increment or decrement heat each tick
• Add field that allows devices to increase or decrease the heat limit for a ship
• Add <OnOverheat> event to ships; this triggers every update if the ship's heat exceeds 100% - if it doesn't exist, then damage ship armour if above 100%, with a chance to damage ship devices and armour if above 150% and chance/damage increasing with higher heat
• Allow players to fire weapons if the ship is overheating, but play a warning noise every time a weapon is fired with the heat at 90% or over - only do this if the last warning is more than 30 ticks ago to avoid spam

[exinfinitum]

I think I'll leave the other planned changes, like overheating effects on ships or devices increasing or decreasing the heat limit, for a future PR.

[exinfinitum]

Note that if #74 is merged this PR will have conflicts that must be resolved. exinfinitum#2 represents how the conflicts should be properly resolved.