[iPad2] Clipping when Air Resistance is off

[arouinfar]

For phetsims/qa#29.

On the Lab screen, if air resistance is off, the Altitude slider's left tweaker and the 'g' in Drag Coefficient are clipped a bit. Turning on Air Resistance fixes the problem.

The same issue effects the 'g' in Drag Coefficient on the Intro screen, but not on Vectors.

The only test device this was observed on was the iPad 2, but @phet-steele also saw it on his external monitor. Perhaps it's related to low resolution?

[andrealin]

@arouinfar , the above commits fix the original issues, although there is still slight clipping on the "A" in "Altitude." Could you review?

[arouinfar]

Reviewed with @andrea-phet and it looks good.