OSM OpenMapTiles style (#1420)

* OpenMapTiles style

* Rename style snippets from layer_name.json to defaultstyle.json

* Add README to icons dir.

* Add README to icons dir.

* Rename snippets to style.json

* Fix spritezero - move icons to svg subdir

* Move icons from style/icons/svg directly to style/icons

Co-authored-by: Tomas Pohanka <TomPohys@gmail.com>

style/style-header.json

@@ -0,0 +1,36 @@
+{
+  "version": 8,
+  "name": "OSM OpenMapTiles",
+  "id": "openmaptiles",
+  "center": [
+    0,
+    0
+  ],
+  "zoom": 1,
+  "bearing": 0,
+  "pitch": 0,
+  "sources": {
+    "openmaptiles": {
+      "type": "vector",
+      "url": "mbtiles:///data/tiles.mbtiles"
+    },
+    "attribution": {
+      "attribution": "<a href=\"https://www.openmaptiles.org/\" target=\"_blank\">&copy; OpenMapTiles</a> <a href=\"https://www.openstreetmap.org/copyright\" target=\"_blank\">&copy; OpenStreetMap contributors</a>",
+      "type": "vector"
+    }
+  },
+  "glyphs": "{fontstack}/{range}.pbf",
+  "sprite": "sprite",
+  "layers": [
+    {
+      "id": "background",
+      "type": "background",
+      "layout": {
+        "visibility": "visible"
+      },
+      "paint": {
+        "background-color": "#f2efe9"
+      }
+    }
+  ]
+}