add power siphon and felstorm conditions to demonology simc

[joshjau]

ported from simc source (sc_warlock_pets.cpp, sc_warlock_actions.cpp):

power siphon:

• prevent core capping before tyrant window
• checks for < 3 demonic cores
• tyrant cd > 25s
• not during demonic power buff

felstorm:

• add cleave logic for fel sunder builds
• requires 2+ targets
• checks demonic strength talent/cd
• requires fel sunder talent

also cleaned up some tyrant timing logic and imp despawn variable tracking