Client|libcommon|Input: Added 'Head Tracker' input device; raw axis mode

There is now a virtual input device for head tracking. It has three
axes with an absolute position and no filtering applied.

Device axes can now be flagged as IDA_RAW, meaning their values will
not be smoothed in any way. Instead, the latest received values are
always used.

Also, with "input-sharp 0", i.e., unsharp input ('sharp' meaning
synchronized with 35 Hz game ticks), player yaw and pitch angles are
updated from the controls on every frame rather than only at 35 Hz.

The Input Settings dialog was updated with toggles for "input-sharp"
and mouse axis filtering.