lib/bb/ui/crumbs/: replace custom HobNotebook

lib/bb/ui/crumbs/: replace custom HobNotebook

The custom HobNotebook widget was implemented to address perceived
deficiencies in the gtk.Notebook API.

Recent inspection reveals that the API is capable of all that Hob
requires of it and therefore maintaining a custom class to provide
similar functionality does not make sense.

Addresses [YOCTO #2276]

(Bitbake rev: e683caa9863bbb52480346669806f22173629a5e)

Signed-off-by: Joshua Lock <josh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>