It is necessary to have it beforehand when creating layout objects
for unselected layouts.
In the current layout system, there is no layout object, but to allow
tabs and dynamic tagging features like ion3, layouts cannot be stateless.
This allow layout "arrange" to be called less often and react on
the cause of the change itself rather than it's consequences
(usually, the "focus" signal).
Previously, the layout were re-arranged everytime the focus changed.
Now, with "raised" and "lowered", it require less "arrange".
"swapped" allow smarted layouts. Currently, swapped cause a full
re-arrange. It re-read the "index" list from scratch and create
a "new" layout. With "swapped", incremental layout changes are
possible.
Fixes https://github.com/awesomeWM/awesome/issues/616
This still does `client.focus = c` by default, but allows to customize
it.
This was initially suggested in #194, but by using `request::activate`
instead, which would not be the same. Therefore a new signal is being
used instead.
Helped-by: Samir Benmendil <samir.benmendil@gmail.com>