Fix get_bindings method

Now it work properly only with domain_id or device_id
Change routing for api methods

Now every binding method is starting with "binding" or "bindings"
"bindings_list" command now should return all binding when there is no
both domain_id and device_id
Add method binding-get which should return details about binding
Merge branch 'havana-rb-vm-bindings' of github.com:slawqo/designate into havana-rb-vm-bindings