Support tile sources without configured projection

This change adds a lot of flexibility to working with tile
layers: Sources where the server projection or tile grid do not
matter can now be constructed without specifying a projection or
tile grid.

The tileUrlFunction/imageUrlFunction now also creates updated
URLs when the params of the layer change, so things like
mergeNewParams in ol2 will be possible.

A nice side effect of this whole change is that there is no more
duplicated code between tiled and single image WMS layers.

While I was at it, I also fixed a WMS 1.1.1 axis order issue
and incorrect STYLES params (STYLES=& instead of STYLES&).

src/ol/source/wms.js

@@ -0,0 +1,37 @@
+goog.provide('ol.source.wms');
+
+
+/**
+ * @param {string} baseUrl WMS base url.
+ * @param {Object.<string, string|number>} params Request parameters.
+ * @param {ol.Extent} extent Extent.
+ * @param {ol.Size} size Size.
+ * @param {ol.Projection} projection Projection.
+ * @param {string=} opt_version WMS version. Default is '1.3.0'.
+ * @return {string} WMS GetMap request URL.
+ */
+ol.source.wms.getUrl =
+    function(baseUrl, params, extent, size, projection, opt_version) {
+  var version = goog.isDef(opt_version) ? opt_version : '1.3.0';
+  var wms13 = version >= '1.3';
+  var axisOrientation = projection.getAxisOrientation();
+  var bboxValues = (wms13 && axisOrientation.substr(0, 2) == 'ne') ?
+      [extent.minY, extent.minX, extent.maxY, extent.maxX] :
+      [extent.minX, extent.minY, extent.maxX, extent.maxY];
+  var baseParams = {
+    'SERVICE': 'WMS',
+    'VERSION': version,
+    'REQUEST': 'GetMap',
+    'FORMAT': 'image/png',
+    'TRANSPARENT': true,
+    'WIDTH': size.width,
+    'HEIGHT': size.height,
+    'BBOX': bboxValues.join(',')
+  };
+  goog.object.extend(baseParams, params);
+  baseParams[wms13 ? 'CRS' : 'SRS'] = projection.getCode();
+  //TODO: Provide our own appendParams function to avoid this empty string hack
+  var stylesParam = 'STYLES';
+  baseParams[stylesParam] = params[stylesParam] || new String('');
+  return goog.uri.utils.appendParamsFromMap(baseUrl, baseParams);
+};