Large Enemy movement

[clintbellanger]

Add functionality to make Large enemies practical, e.g. enemies that require two-tile-wide corridors for movement.

Probably the best way to implement this is to add a collision radius to enemies. A two-tile-wide enemy in the current data might have a radius of 48, so they're unable to pass through a single-tile (64 units) space.

Hazards would need to consider this radius.

[clintbellanger]

Removing this from the v0.16 milestone. It's not strictly necessary, and it's something we can revisit later (especially if we address having enemies/heroes collide with each other).

[igorko]

Migrated to clintbellanger/flare-engine#128