Replace dat.gui with Bootstrap

[bhowes-tt]

dat.gui is a bummer on a tablet or a phone. It has it's advantages, but the time has probably come to move on :[

I'm just starting to mess with bootstrap on some other projects, and it feels pretty awesome...

On a separate branch, attempt to replace dat.gui with bootstrap, including the sliders. Also try to clean up some of the additional divs we need - loading, attributes, file open, etc

[mnaugle-tt]

ahhh i could not agree more with this move. dat bums me out. i think bootstaps will make customization much easier too.

[bhowes-tt]

I'm into it too.

We'll have to do some experimenting with bootstrap. I think it might be harder to make it work in embedded viewer scenarios... I'm worried about it trying to take over the host page's styles. But we'll see.