Set now to 1e-6. We probably should not go above.

This non-atomic commit (which is bad) fix the following problems:
- Improve the stopping phase.
- Remove useless m_Q
- Remove useless BuildingConstantPartOfTheObjectiveFunctionQLD
and useless BuildingConstantPartOfTheObjectiveFunctionQLDANDLQ
- Rename Problem_s in ProblemVelRef_s

The scheme changed because the height of the CoM is not 0.814
from Kajita's book, but the real CoM height computed for the robot.
It changes slightly the numerical result.

O2 with -DNDEBUG is faster than O3 and previous flags
on a Xeon 3.2 GHz with 2Mb of L2 cache.

The flags needs further investigation.

Conflicts:
	tests/CMakeLists.txt