Nice! I love this balance tweak! And it can be changed depending on how
strong we want it to be.

The impulse is fairly weak, but it has no cooldown (of course). As long
as you can reliably click on them, you can keep dragging them around.
This builds charge.

Portal now COSTS charge, rather than gaining it, so that you bully
people until you can build a portal.

You touching a wall does not do it. This encourages teamwork / using
your walls in clever ways to gain charge.

Also allow 100 walls, and removal of all walls upon death

This reverts commit f41676c672.

I misunderstood the way the camera projections work, and I'm better off
using the original raycasting strategy.

And Camera.project_ray_normal. This is much better

Also, levels now inherit a level object

In multiplayer, if there is only one hero 1, it is ok, but with more
than one, one hero 1 cannot place walls.