add structured summarizes directory

[andibraeu]

the collector should be able to create a summarized directory, e.g. grouped by the field meta community in the following format:

{
  community1 : {...},
  metacommunity1 : {
    community2 : {...},
    community3 : {...}
  },
  community4 : {...},
  metacommunity2 : {
    community5 : {...},
    community6 : {...}
  }
}