Only activate whitespace-mode in editable buffers
Only activate whitespace-mode in editable buffers

Otherwise whitespace-mode will disrupt fontification in special buffers,
like helm and elfeed buffers.

Indirectly addresses #1179

UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/doom-emacs,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/doom-emacs