Fix some enemies not going down slopes

[MatusGuy]

Some enemies with big hitboxes didn't go down slopes. This was because the max drop height was too small. The max drop height for smart enemies is now width / 2.

I also added LedgeBehavior, which can be used with WalkingBadguy::set_ledge_behavior, instead of setting numbers like -1, 16 or 600

[MatusGuy]

AWit what

[Rusty-Box]

Since you set it to "draft" you still want some reviews or... we wait with that?

[MatusGuy]

I set this to draft because something went horribly wrong with the Git side. I'll fix this shortly

[MatusGuy]

Should be good now

[tobbi]

Very good PR, a-ledge-edly.