Add analysers to calculate Integral of resource usage

[VincenzoFerme]

Some details about the data we are going to integrate:

The data are sampled every second.

Some references:

• Different type of integrating sampled data: http://dmpeli.math.mcmaster.ca/Matlab/Math4Q3/NumMethods/Lecture3-4.html. The Trapezoidal rule seems suited for our case.
• A python library enabling the computation of integrals: http://docs.scipy.org/doc/scipy-0.14.0/reference/integrate.html