Boxes overlap

[KatieWoe]

For phetsims/qa#221. Likely connected to #81. When stringTest=double but not long the Charge 2 box and the Force values box overlap. Discovered on an iPad, but occurs elsewhere. See image bellow.

[arouinfar]

Good catch @KatieWoe!

Comparing Macro Scale to Atomic Scale, it seems that the problem is that the Charge panels haven't been given a maxWidth. Macro scale has longer units (μC) compared to Atomic Scale (e), which leads to a wider panel.

However, I'm not so sure the Charge panels need to expand at all, since there's quite a bit of white space around "Charge".

[KatieWoe]

1.0.0-rc.6 looks good.