large chunk of work towards a nicer build system

- plugins are now parsed for @@..@@ replacements
- main script and plugins have separate .meta.js files created - less web server load for update checks
- build script has variables for resource URL, update URL, etc, substituted via @@..@@ into main script and all plugins

external/leaflet.css

@@ -285,7 +285,7 @@
 	        border-radius: 8px;
 	}
 .leaflet-control-layers-toggle {
-	background-image: url(http://iitc.jonatkins.com/dist/images/layers.png);
+	background-image: url(@@RESOURCEURLBASE@@/images/layers.png);
 	width: 36px;
 	height: 36px;
 	}