naughty: resize naughtifications to the minimum needed space
This commits adds support for :extents() to naughty. It changes the
behaviour of naughty.config.presets.*.width so that if it's set to nil,
the notification gets resized automagically. Else the value of width is
used for the notification's width.
The meaning of naughty.config.presets.*.height changed similarly, now,
if set, it means the literal height of the notifications. If unset, the
notification gets resized automagically as well.
Signed-off-by: Gregor Best <farhaven@googlemail.com>
Signed-off-by: Julien Danjou <julien@danjou.info>