Mob randomization

[Pjiwm]

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Mobs should have random aspects about them, right now most of them just get a speed or strength boost,
this will be changed with random effects and attribute changes.

Please provide enough information so that others can review your pull request:

There needs to be a general random boost and a specific one for certain mobs such as creepers.
The following features will be implemented

• a generic mob buff method that randomizes health attributes and effects
• unique skeleton arrows
• random creeper explosion size
• random charged creepers
• random slime sizes
• super mob with even higher effects and glowing effect
• ghast higher explosions

Explain the details for making this change. What existing problem does the pull request solve?

We solve predictable mob patterns with randomization, players will never be sure how strong a certain mob is when fighting.

Test plan (required):
Demonstrate the code is solid. Example: The exact commands you ran and their output, screenshots / videos if the pull request has visual changes.

1. Run local server
2. Create a redstone clock that summons mobs with a command block.
3. Check if randomization and new features work.

Closing issues
closes #19

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