Support single-vocabulary Terminology Providers via config file

[nichtich]

For instance like this:

[
  { "url": "//api.dante.gbv.de/" },
  {
    "voc": [ {
      "uri": "http://bartoc.org/en/node/430",
      "prefLabel": { "de": "Gemeinsame Normdatei" },
      "notation": ["GND"]
    } ],
    "data": "http://coli-conc.gbv.de/services/gnd.php",
    "suggest": "https://ws.gbv.de/suggest/gnd/?searchterm={searchTerms}"
  }
]

The voc service is hard-coded with a fixed result set. The data service is given with base URL, for instance http://coli-conc.gbv.de/services/gnd.php?uri=http://d-nb.info/gnd/1-2. The suggest service is given with URL template. Other services (top, ancestors) are not supported.

[stefandesu]

This can now be tested on branch api-overhaul. I'll leave this issue open as there's still some refactoring and cleaning to be done on this.