Add lfixed layout.

Puts a fixed-width client to the left and bstack to the right.
=> Handy for developing in a terminal in the master and having a decent
   layout to the right.
=> Shamelessly stolen from my friends who've got this layout in xmonad.
Modify fixed layout logo; add a column more.

Syntastic plugin for vim actually uses two columns for the leftmost
error indicator column.