factor out renderclients

This will help once we get to implementing layer-shell

don't autoraise

Still raise in buttonpress and focusstack of course.  Focus models
honestly wouldn't be too hard to make into a config.h option.

use the focus stack to determine stacking order

Suddenly we have autoraise!

adopt a bit more dwm-like terseness

change focus(NULL, NULL) to mean unfocus

"Focus the most recently focused window on selmon" is now refocus()

implement focusmon and tagmon

focus follows mouse

add incnmaster and setmfact commands

add toggletag and toggleview

don't detect non-visible clients under cursor

add tag and view functions

refocus if focused client is unmapped

focus(NULL, NULL) works like dwm's focus(NULL): focus the most recent
visible client on selmon, or clear the existing focus if there are none.

implement floating windows

load scaled cursor theme with each output

turn focusnext into dwm's focusstack

restrict focusnext to the same monitor

style

add selclient() helper

This may get inlined later, but it's nice for now.  The focused client
if any should always be both at the top of fstack and visible on selmon.

continue to focus monitor under mouse cursor

focus monitor under mouse cursor initially