Clean up PushOutEnemy logic

[eric62369]

• [x] what happens if multiple enemies interact with the PushOutBox?
• [x] It is still possible to stack characters, which shouldn't happen
• [x] Jumping into a character in the air should repel the characters from each other slightly
• [x] Try looking at this again: https://answers.unity.com/questions/825803/trigger-2d-repel-on-overlap-2-d-player-combat-issu.html

New Design: Pushbox script will exist to prevent stacking as well as falling through ground How to prevent going through walls? Retain left and right one way pushboxes (prevent wall passthrough) Retain parent ground onewaypushbox (prevent ground passthrough)

New opponent pushbox style: Repel in X direction

• [x] Don't think about groundedness