`trigger_heal` improvements

[jjelliott]

trigger_heal could use the following additional features:

• Health limit
• Amount to recharge
  • Say a pool has 400 health, but it will recharge 5 health every 10 seconds if it's below "full".
  • default 5
• Recharge wait
  • interval between recharges
  • default 10s
• Recharge delay
  • how long after healing to wait before starting to recharge
  • default 10s