Need discrete mode attack and use commands

[timhutton]

Currently there's no way to build with discrete actions.

A partial workaround is to use both DiscreteMovementCommands and ContinuousMovementCommands (with a deny list to avoid the conflicts) and then use the attack and use that come with the continuous mode. But this makes tricky issues about the timings of the duration of the actions.

Needed by @geekstor for building tasks.

[timhutton]

Actually there's a few things we might want to change in the discrete movement commands:

• no strafe command
• the pitch command is called look for some reason
• jump command is odd since agent falls - should be jump_forward?