Automatically expand content to fill remaining space

[choldgraf]

This PR removes all of the explicit col widths of the "main" content section, and replaces them with a single col class, which bootstrap will use to expand to take up whatever remaining space exists on the page. I think this simplifies how things work a bit, and we get the bonus of not worrying that the main content isn't filling up the space available to it.

It also adds an overflow class to make sure that content is properly wrapped

[jorisvandenbossche]

This probably might conflict with #134 ?

[choldgraf]

maybe, does @hoetmaaiers know? This PR was mostly trying to do a surgical fix on a bug, and a slight simplification in the logic for the width of the main content. If the same thing is being implemented over in #134 I'm fine to close this...

[choldgraf]

closing this as I think it's been superceded