Add a dead zone configuration for controllers

[krichardsson]

Some joysticks/controllers have noise in the values which might cause drift over time. One solution would be to add a dead zone in which the input is ignored.

Preferably the zone should be configurable.

Related to #47

[tlwmdbt]

In Windows 7 the standard Joystick helper programs deadzone configuration is over ruled by the Crazyflie client. I have heavy noise on my new Joystick and my Xbox Controller is unusable. I cannot start the Crazyflie without drifting heavily to the noise middle. A deadzone control would really be appreciated. It's not just an overtime effect for me. I cannot use it like this. My XBox Controller has a neutral position somwhere between -/+ 10 in the X and Y axe (I cannot fly straight up).

[Mitteau]

Yes, very useful because the precision of a joystick is highly variable, around null position. Very easy to implement.

[Mitteau]

I am testing the implementation, see my branch "nexon" from a fork of python client. My repo is Mitteau/... Do I ask for a request to pull? I use also an xbxo360 controller. My dead zone is +- 0.08. A dead band is very confortable for stationnary flight and progressive take off.

[Mitteau]

Bug if there is no input map...

[Mitteau]

Looks OK now...

[Mitteau]

Pull request proposed.

[krichardsson]

Implemented in #332