Cleaning of BodyPairContact usage

[EulalieCoevoet]

The way the list bodyPairContacts was filled and used was a bit confusing to me.

Changes:

• I moved relativeVelocity, relativeAngularVelocity, computeRelativeVelocity(), getRelativeKineticEnergy() from Contact to BodyPairContact. The relativeKineticEnergyHist list, checkRelativeKineticEnergy() were already there, so I was wondering why not everything related?
• I got confused by the boolean BodyPairContact.updatedThisTimeStep, and by what is in CollisionProcessor.bodyPairContacts exactly... So I tried to clean/refactor everything related to this list.

Question:

• I feel like BodyPairContact.updatedThisTimeStep is mostly used because the list CollisionProcessor.bodyPairContacts may contains empty BodyPairContact. Am I right?

Missing:

• I would like to remove BodyPairContact.updatedThisTimeStep and simply make sure that the list CollisionProcessor.bodyPairContacts is up to date.

@otmanon: Am I missing something here? I feel like this is an important cleaning. I may be wrong... Anyway I look forward to talk about that.

[EulalieCoevoet]

So I went further into the cleaning, managed to remove updatedThisTimeStep boolean. Everything seems to work correctly, yet I'd like to review these changes with you Otman (on Monday maybe).