feat(boss): implement almost-full boss

[olivierperez]

Description

Closes #48 - Base mechanics of a boss enemy

• Create a Boss node inherited from Mob
• Import assets and add credits
• Implement some mechanics and transition between them
  • Wait for players
  • Follow players
  • Attack (no damage for now)
  • Spawn minions
  • Die

Motivation and Context

We need a boss with mechanics.

How has this been tested?

In DebugLevel.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the credits
• I have updated the credits accordingly.

[PopsIDX]

Did you try multiplayer on this boss ?

[olivierperez]

@PopsIDX I've made some fixes so the Boss can actually detect players added to "Players" node, otherwise he didn't detect them.
For the remaining about the multiplayer-thingy, I would like to wait we handle the sync of mobs before doing specific things on boss (as he inherits form Mob).