feat: Generic Enemy

[doblesantos]

An extendable class for any Enemy

[erickgomez28]

First requirements:

• The enemy should appear every so often (and it must not first collide with the fungus)
• When the enemy appears attack the nearest fongus
• When the enemy collides with the fungus, that fungus and its roots are removed
• If the fongus don't have effects the enemy stays alive and attacking