openbox: add run time dependency on openbox-theme-clearlooks

Without this default theme install , openbox is unable to start, and shows the
following message:

dragonboard-410c:/home/linaro# openbox
ObRender-Message: Unable to load the theme 'Clearlooks'
ObRender-Message: Falling back to the default theme 'Clearlooks'
ObRender-Message: Unable to load the theme 'Clearlooks'
Openbox-Message: Unable to load a theme.

As discussed in [1] , the solution is to make sure that openbox-theme-clearlooks
is always included.

[1] https://www.mail-archive.com/openembedded-devel@lists.openembedded.org/msg47153.html



Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>