* gluon-core, gluon-client-bridge: introduce new firewall zone: local_client
 * gluon-core: put clients in local_client zone, introduce drop-zone,
   set dns-rules and zones
 * gluon-respondd: allow respondd on mesh
 * gluon-status-page-api: allow http input on mesh and client

Some files have received some additional refactoring.

gluon-mesh-babel is not merged yet, and once it is, this would lead to a
circular dependency.