Reorganized the code into a proper library

The compilation now produce a 'libfacetracking.so' and
a 'facetracker' binary.

To this end, facetracking.cpp has been split into main.cpp and
facetracking.cpp.

While here, several other minor changes/tuning, including:
 - installation of the haarcascade trained database stolen from opencv.
 - get rid of the ROS generated CMakeLists. It is now a simple and
   regular CMakeLists.
Initial scaffolding for automatic testing

Currently only plays and detects faces on a single pre-recorded video.