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/config.json

@@ -0,0 +1,22 @@
+{
+  "options": {
+    "paths": {
+      "fonts": "/data/fonts",
+      "sprites": "/build/style",
+      "styles": "/build/style"
+    }
+  },
+  "styles": {
+    "OSM OpenMapTiles": {
+      "style": "style.json",
+      "tilejson": {
+        "type": "overlay"
+      }
+    }
+  },
+  "data": {
+    "openmaptiles": {
+      "mbtiles": "/data/tiles.mbtiles"
+    }
+  }
+}