Overlay previews (leaflet-extras#270)

* New maps: OpenPtMap, OpenRailWayMap, SafeCast added

* OpenFireMap added

* Fix test errors (colon position)

* Fix zoomlevel in OpenPtMap layer

* Allow double quotes in JSON (standard)

* Soooory, revert in lint definition

I just was in the wrong branch :-(

* Preview as overlay (OIM, OPM, ORM, OFM, SC)

OpenInfraMap, OpenPtMap, OpenRailwayMap, OpenFireMap, SafeCast

preview/preview.js

@@ -63,7 +63,12 @@
 			'Stamen.Toner(Hybrid|Lines|Labels)',
 			'Acetate.(foreground|labels|roads)',
 			'Hydda.RoadsAndLabels',
-			'^JusticeMap'
+			'^JusticeMap',
+			'OpenInfraMap.(Power|Telecom|Petroleum|Water)',
+			'OpenPtMap',
+			'OpenRailwayMap',
+			'OpenFireMap',
+			'SafeCast'
 		];
 
 		return providerName.match('(' + overlayPatterns.join('|') + ')') !== null;