Use lists for `targets` field in JSON source file

[eddowh]

Right now JSON source files are structured like below:

{
    "foo": {
        "target": "https://foo.bar/",
        "uuid": "foo:bar",
        "modname": "foo.bar",
        "tz": "Foo/Bar"
    }
}

However there are some sources that do not store all their information in one single url, for example look at some of the tceq.tx.gov sources for the city Austin:

http://www.tceq.texas.gov/cgi-bin/compliance/monops/daily_summary.pl?cams=1068 http://www.tceq.texas.gov/cgi-bin/compliance/monops/daily_summary.pl?cams=0003

(There are many more.)

There is no single URL which contains all the information for all the stations, hence I propose from now on, for all sources, that we structure the target field as a list and rename it to targets, like below:

{
    "foo": {
        "targets": [
            "https://foo.bar/abc",
            "https://foo.bar/mno",
            "https://foo.bar/xyz"
        ],
        "uuid": "foo:bar",
        "modname": "foo.bar",
        "tz": "Foo/Bar"
    }
}