new config variable scanDelay to add some time between two scans

src/quagga.js

@@ -360,6 +360,7 @@ function workerInterface(factory) {
     var imageWrapper;
 
     self.onmessage = function(e) {
+        setTimeout(function() {
             if (e.data.cmd === 'init') {
                 var config = e.data.config;
                 config.numOfWorkers = 0;
@@ -375,6 +376,7 @@ function workerInterface(factory) {
             } else if (e.data.cmd === 'setReaders') {
                 Quagga.setReaders(e.data.readers);
             }
+        }, Quagga.getConfig().scanDelay || 0);
     };
 
     function onProcessed(result) {
@@ -516,5 +518,8 @@ export default {
     },
     ImageWrapper: ImageWrapper,
     ImageDebug: ImageDebug,
-    ResultCollector: ResultCollector
+    ResultCollector: ResultCollector,
+    getConfig: function getConfig() {
+        return _config;
+    }
 };