Support array of sensor IDs in query

[Sascha Steinbiss]

It would be desirable to support querying for multiple sensor IDs in the GraphQL frontend, e.g.:

query {
  entries(rrname: "test.foobar.de", sensor_id: ["abcde", "fghij"]) {
    rrname
    rrtype
    rdata
    time_first
    time_last
    sensor_id
    count
  }
}

where the result would be a union of the results for all sensors in the list. The limit parameter would then apply for this merged result.