Switch to scala-maven-plugin instead of maven-scala-plugin to be
compatible with m2eclipse-scala and so remove recalcitrant warning

Add to README file how to use PowerAPI with the Eclipse IDE
Sensors: factorize Tick listening in defining the acquire process to the
parent type fr.inria.powerapi.core.Sensor
Remove unecessary tests from Sensors API
New Sensor, sensor-powerpy, monitoring power values provided by the
bluetooth powermeter PowerSpy
(http://www.alciom.com/fr/produits/powerspy2.html)