Add more configuration options to Effect system

[sh0ckR6]

The effect system as it currently stands feels a little static. There's not really much room for customization, and I think some more configuration options would be beneficial.

New proposed configuration options:

• Whitelist/Blacklist certain potion effects
  • If a whitelist is defined, all other effects will be implicitly blacklisted.
  • If a blacklist is defined, all other effects will be implicitly whitelisted.
  • There cannot be both a blacklist and whitelist.
• Individual settings for each potion effect
  • Any setting not explicitly defined will use defaults
• Option to override the failsafes added for the Wither and Instant Damage effects
  • These were implemented so the player couldn't instantly die to these effects

Example of how this could work:

effects:
  allowed:
    - instant_health:
        amplifier:
          max: 15
          min: 5
        duration:
          max: 60
          min: 1
    - "speed"
  denied:
    - "wither"
    - bad_omen:
        amplifier:
          max: 2
  # Note: "allowed" and "denied" cannot be defined at the same time and are only both here for demonstration
  # Potentially send an error message to the user when loading configuration stating that both "allowed" and "denied" are both defined