Reactor balance in 'off' state + various fixes

Updated reactor to remain active after chunk (un)loading
Fixed reactor energy output too low at high instability
Reduced reactor initial production
Adjusted number of laser packets per cycle
Improved reactor robustness (protection for negative energy, etc.)
Fixed reactor API so computer gets current parameters
Fixed reactor API returning output rate per cycle instead of per tick
Refactored reactor mekanism (mode encoding, random number,  energy
generation & side textures refresh)
Fixed reactor recipes