Physical instability of model

[piotr-marcol-tpx]

It was observed, that certain parts of the model show some kind of shivering. Especially:

a) Wheel contact points:

b) Shaking inertias of front wheels/steering wheels system:

These issues may, but not necessarily, be associated with each other. One of the suspects is low mass of the links, which may cause numerical instability in simulation, but rear wheels do not show the shivering mentioned in b).
The issues were initially introduced in #2, but since debugging of these phenomenons is probably more time-consuming and low-level, so in order not to block remaining improvements/fixes from #2, they were separated out to this very ticket.