Add 'hidebydefault' option for Markers layers

src/main/resources/configuration.txt

@@ -47,6 +47,8 @@ components:
     #showlabel: true
     # If set, enables support for using signs for markers
     #enablesigns: true
+    # If set, make markers layer hidden by default
+    #hidebydefault: true
     
   - class: org.dynmap.ClientComponent
     type: chat

web/js/markers.js

@@ -70,6 +70,7 @@ componentconstructors['markers'] = function(dynmap, configuration) {
 	function createMarkerSet(set, ts) {
 		set.layergroup = new L.LayerGroup();
 		set.timestamp = ts;
+		if(!configuration.hidebydefault)
 			dynmap.map.addLayer(set.layergroup);
 		dynmap.layercontrol.addOverlay(set.layergroup, set.label);
 	}