To be fully responsive, we can basically never specify the width of
our container in a fixed number of pixels; otherwise we'll run into
the situation where there's an inordinate amount of wasted space on
our left and right.
So everything needs to change from, e.g. row to row-fluid,
and that has a whole cascading series of changes that that implies.
(imported from commit 7e2771d916f429548c65c0a00fc4c11397054656)