b2RigidPlasticJoint moment and force are not correct for additional mass

[simo-11]

• test without warm starting
• modify joint so that contacts are taken into account without warm starting
• handle initial rotational velocity in some other way
• figure out other options if needed

adding directly above beam's center of gravity (x=10), gives correct result.
e.g. 500 000 kg causes additional force of 5 MN and 5 MNm so that total force 8 MN and moment 81.2 MNm
for x=9 total force is 9 MN and moment 91 MNm
for x=8 total force is 11 MN and moment 101 MNm
for x=11 total force is 7 MN and moment 71 MNm
for x=12 total force is 5 MN and moment 61 MNm
for x=13 total force is 3 MN and moment 51 MNm but system is drifting #16 fixed drifting
for x=16 total force is ~ 0 MN and moment 24 MNm
fro x=19 total force is -5 MN (negative) and moment -6-10 MNm (correct moment is 126 MNm)

Impulse from additional mass is handled as if there was joint at center of gravity.

for x=8
with rp

with ep using 10Hz

[simo-11]

contactSolver.WarmStart causes too large velocity/impulse which is normally corrected during iteration but not in rigidPlastic processing.

x	vy	va
10	-0.42	0
19	-0.35	-0.049

RigidPlastic does not currently work at all with contacts if warm start is not active.