Tracking

Commercial message: improve the processing rate by 1000% !

Technical message: integrated opencv's tracking feature into Chilitags. A call to the "track()" method can replace one to find(). It is a lot faster (4ms with one tag on a 1600x1200px image with a laptop processor, versus ~35ms), but can not detect new or disappeared tags.

Tracking can also improve a little the detection, for tags that are moving to fast for find(). Such improvement can be toggled with setFindAndTrack()

Not propagated into the 3D part yet. Not tests either, but a sample.

This branch is based on https://github.com/qbonnard/chilitags/tree/performance_tuning