fix crash when setting a custom mode

rework outputmgrapplyortest()

first disable requested monitors, then enable and/or change mode, x and y, etc.
This is mostly what sway does

check client_from_wlr_surface() returning NULL in urgent()

fix #281

fix segfault if parent->mon is unset

use the layer surface to create popups

make sure we do not create a double fullscreen_bg

and also make sure we do not destroy it if it does not exist
Fixes: #274

conform the xdg-protocol with fullscreen translucent clients

see `setfullscreen()` for more info

always set the same monitor and tags for child clients of a client

fixes #272

do not focus clients if a layer surface is focused

force line-buffered stdout if stdout is not a tty

Revert "only call wlr_seat_keyboard_notify_enter() if a keyboard is found"

This reverts commit 8e03bce6217117f0687cd727ae2c47bdd3c0fe5a.
fixes #270

only call wlr_seat_keyboard_notify_enter() if a keyboard is found

check pointer focus in arrange()

arrange client's monitor if size has change since last commit

resize now takes `struct wlr_box` as parameter

check current and pending geometry to set c->resize to zero

Fixes #260

Checks for overflows for client max width and height

respect size hints

inline unmaplayersurface() into unmaplayersurfacenotify()

unmap signal is guaranted to be emitted before destroy signal
so is useless checking if it is mapped at destroy

avoid layer surface popups appearing below x{dg,wayland} clients