Prompts for an open project and kills all its buffers. This is useful
for closing `.emacs.d` in an effort to get some *billable* work done.
Added `doom-fixup-windows` and `doom-kill-buffer(s)-fixup-windows`
helper functions for leaving affected windows on a real buffer or the
fallback buffer.
Fixed `doom/kill-this-buffer-in-all-windows` to properly "fixup"
windows.