Engineer gameplay improvements.

[ghost]

As-is, the engineer does not propose very interesting or enjoyable gameplay. In particular:

It's quite hard to build walls properly quickly, especially from cover. My suggestion would be to, instead of just gluing a cube to the face hit, have it follow some simple physics-like rules, such as:

• when a wall is hit the cube would "climb" one block in the direction it was flying (so the player does not have to aim on the top face);
• otherwise falls down one block if there's resting ground available there.
  Those rules would make it easy to quickly build walls for cover aiming roughly at constant height, but not interfere with e.g. building bridges.

The weapon does not seem to affect enemies. If it's not supposed to have actual damage, I'd suggest knocking enemies back (perhaps causing damage if they hit a wall).