nodeinfo: mesh interface classes (wireless, tunnel, other)

This will introduce a new nodeinfo object, network.mesh.bat0.interfaces,
containing any of the the following subordinated objects:

- wireless
- tunnel
- other

Each of these objects contains a (possibly empty) list of MAC addresses
(lowercase, colon-notation) corresponding to a interface of the given
class. Combined with a batman graph it is thus possible to mark
sub-graphs as "wireless" or "vpn".

The previously used object mesh_intefaces is superseded by this new
object structure and mesh_interfaces will be removed in a future Gluon
release.