Set a limit on number of glyphs to render in visbol

[cjmyers]

Add a limit to the number of glyphs to render (default 30) to address problem with large, flat genome representations reported in SynBioHub Issue #626.

[dany-fu]

Should there be an option to expand the rest of the representation? And if there is, should the rendering just continue on the same line or further down the page?

[cjmyers]

The problem is it could be too large to expand completely. There is another option #74 which gives the idea of "paging" through the visualization.

We might want to try to be more clever about what we hide. I think I will log another issue about this.

@jakebeal may have other thoughts on this.