Support longer JS interactive examples

[wbamberg]

Currently, with the JS editor, if an example has more than 12 lines, the editor overflows and gets a scrollbar. 12 lines is a good maximum for most cases, but sometimes we really want to go over 12 lines. In these cases, it would be better to make the editor bigger, to avoid scrollbars.

We could support this by letting the EmbedInteractiveExample macro take a parameter asking for more space, and passing it on pages which need it.