Improved server browser + new items

The main change in this update is a new steamworks based server browser. It should find games faster and more reliably.

Also added a few items: -Magnetic ammo for bombs/mines. It drifts towards nearby enemies. -Safety ammo for most projectiles, which reduces self/friendly fire damage. -Trident mod is now a barrel rather than an ammo type, allowing you to combine it with singularity warheads etc.