set `c->prev` in setmon() and not in mapnotify()

only enable/disable clients from the specified monitor in arrange()

also fix a crash when m is null, this can only happen when selmon is NULL

set c->prev in mapnotify()

Closes: #300

Minor changes to README

Add direct irc link

Also, move IRC section to the top so that it's more accessible.

don't arrange layers on disabled monitors

call setfullscreen() in setmon()

this will help when sending to another monitor a fullscreen client
and also will prevent a crash when a client request fullscreen when it has no monitor

prevent segfault when destroying monitors

also don't count unmapped surfaces for exclusive zone
and exclusive_focus is now of type `void *`

Revert "Revert "various improvements to layer surface""

This reverts commit c017916d35795cf85e5181907f5e97a1d702612a.

Revert "various improvements to layer surface"

see https://github.com/djpohly/dwl/issues/289#issuecomment-1231287114

This reverts commit 226051974060746d02d787ac1ef70b6267ee51b4.

various improvements to layer surface

- remove various useless assignments of layersurface->mon
- styles changes
- do not set wlr_layer_surface->output to NULL at destroy

conform the idle inhibitor protocol

previously we disable idle tracking simply due to the fact that it exist

new function to notify keyboard enter

sort client.h functions

prevent an infinite loop if try to use focusmon() with all monitors disabled

don't try to set monitor for clients in createmon()

this is done in updatemons()

set monitor for clients that don't have one in updatemons()

only if selmon is enabled and the clients are mapped

set monitor for clients that don't have one on monitor creation

don't respect size hints for fullscreen clients

Fixes: #292

change type of c->bw: int -> unsigned int