UX: Backlog: Remove extra whitespace

Prepare for making our design responsive
by removing the whitespace that is not
necessary, and in the meantime adding
a few css classes to help us debug
the layout.

This commit is primarily a work in progress.
Fix: UX: Do not highlight active navbar item

This was a regression in the migration to
Bootstrap 3.
UX: Backlog: Center the story list

Clean up the grid layout of the backlog,
removing most of the css margins, so that
the story list is centered and the
whitespace is even on both sides.

We're at a good point now for adapting the
story list to different screen sizes.