Give all platform blocks in submission page equal height (bug 964961)

https://bugzilla.mozilla.org/show_bug.cgi?id=964961

Tested with IE9 and more recent browsers. I don't have Safari though.

Screenshots with Firefox:

![normal](https://cloud.githubusercontent.com/assets/187006/4337018/b66c353a-400b-11e4-89f5-ecf0275c3f8d.png)
![with custom error message added](https://cloud.githubusercontent.com/assets/187006/4337043/dba02e60-400b-11e4-914c-8797a359aa74.png)




wrap isn't supported until Firefox 28, is that an issue? I'm assuming this won't work without it since it will try and put the error message and change to free/paid links on the same line.