Change default time in force integration

[marinlauber]

In the pressure force integration the default is to use t=0 for the body position, but this doesn't correspond to the pressure, which is stored at time(sim).

I think the default behavior should be to measure the body at time(sim), where the pressure is also defined. This would require passing sim or flow directly to the function.

[b-fg]

Sure, make a PR and I will review it :)

[weymouth]

Did this get done?

[marinlauber]

No, I haven't done it. I am not sure how to pass the correct time to the function without changing the function arguments.