Sp6.sc1.history search list of streams

Added the _history call.

Example usage: "localhost:8000/_history?stream_id=1,2,3"

That will return the json object:
{
    "history": [
        {"stream_id":"1", "data":[{"timestamp":"TIMESTAMP1", "value": VALUE1}]},
        {"stream_id":"2", "data":[{"timestamp":"TIMESTAMP2", "value": VALUE2}]},
        {"stream_id":"3", "data":[{"timestamp":"TIMESTAMP3", "value": VALUE3}]}
    ]
}

Assuming that stream 1, 2 and 3 have one datapoint each.