Merged 'benchmark' and 'integration' tests
Added minimal unit tests for Objects

Also made the corner coordinates coherents for freetags, indepently of whether
objects are detected or not; in the former case, the origin of the marker was
its center, in the latter, the top-left corner. Now the origin of the marker
is the top left corner in both cases.
Added a sample to visualise the 3d pose estimation
Extracted Estimator out of Objects