Change logger configuration

Currently plugin-specific logging configuration expects a logging keyword in the plugin config, but some plugins might expect a list as top-level config, in which case logging config can't be specified.
Possible solution is to move logging keyword from plugin to global logging keyword in pdi config.
E.g.

pdi:
  logging:
    level:
      global: off
      flowvr: debug
...
  plugins:
    flowvr:
      ...