Resolve "Wago group feature"

Closes #760 (closed)

Config:

- name: wago_group
  plugin: bliss
  module: wago.wagogroup
  class: WagoGroup
  wago:
    - name: $wago_simulator
      logical_keys: foh2ctrl, esTr1, esTr2
    - name: $wago2

API:

• wago_group Show keys, wago name, current value and description
• wago_group.logical_keys key list
• wago_group.cnt_names counter names
• wago_group.counters counter namespace
• wago_group.set('key1', val1, 'key2', val2) set keys
• wago_group.get('key1', 'key2', ...) get key values