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/icons/christian.svg

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   xmlns="http://www.w3.org/2000/svg"
+   version="1.1"
+   width="16"
+   height="16"
+   viewBox="0 0 16 16">
+  <rect
+     width="14"
+     height="14"
+     x="0"
+     y="0"
+     id="canvas"
+     style="fill:none;stroke:none;visibility:hidden" />
+  <path
+     d="M 7,0 C 5.999999,0 6.000001,1 6.000001,1 L 6,4 2,4 l 0,2 4,0 1e-6,8 2.000001,0 -1e-6,-8 4,0 0,-2 -4,0 0,-3 c 0,0 0,-1 -1.000001,-1 z"
+     id="christian" />
+</svg>