Implement a Nominatim geocoder based on the OpenLayers geocoder.

The only difference is in the method used to load data from Nominatim.

OpenLayers geocoder uses OpenLayers.Request.GET(). This geocoder tries to use jQuery.ajax if available, then OpenLayers.Request.GET if available, and falls back to plain XMLHttpRequest.

The usecase I'm thinking about is if one is already using jQuery while using some other map provider (that does not have a geocoder?). There should be no need to load OpenLayers library (which is just too heavy) in such situations.

Or if one does not care about very old browsers, he does need even need any hacks or workarounds and can use just plain XMLHttpRequest.

This file uses CRLF line terminators, like mxn.openlayers.geocoder.js. There seems to be a mix in the repo, but I decided not to touch mxn.openlayers.geocoder.js and keep mxn.jquery.geocoder.js also CRLF to ease diffing between them (yes, I know about the --ignore-all-space flag).

If you want LF line terminators for all new files, you can change that.

This is a redo of #245.