Better encapsulate logic for configuring admin lookup

[orangejulius]

Currently, any importer that uses admin lookup has to make decisions about how exactly admin lookup is performed. For example we currently support admin-lookup via a local set of node processes, or a remote HTTP server.This can be configured in pelias.json, but checking the config settings is currently only done in the importers.

While we definitely want to support different ways of doing admin lookup, figuring out which method to use, and setting it up, should be done within this module, so that importers don't need to care about it. Right now, a bit too much work has to be done by the code calling this module. For example, most of our importers have code similar to this right now:

var through = require( 'through2' );
var logger = require( 'pelias-logger' ).get( 'openaddresses' );
var peliasAdminLookup = require( 'pelias-wof-admin-lookup' );

function createAdminLookupStream(enable) {
  if (enable) {
    logger.info( 'Setting up admin value lookup stream.' );
    var pipResolver = peliasAdminLookup.createLocalWofPipResolver();
    return peliasAdminLookup.createLookupStream(pipResolver);
  } else {
    return through.obj(function (doc, enc, next) {
      next(null, doc);
    });
  }
}

Ideally the var pipResolver line could go away, and any configuration would be passed in without actually having to know as much about the module internals.

Related: #51

[orangejulius]

@dianashk also proposed a similar improvement to the interface in #48 (comment)

[orangejulius]

This was fixed in #89

Creating an admin lookup stream for an importer is now as simple as

const adminLookup = require('pelias-wof-admin-lookup');
adminLookup.create()