Move 'use strict' to file level

Change-Id: I1f0dae4aa168e77c112bcd3688c98b84e4ce5f36
diff --git a/dev/js/src/plugin/client.js b/dev/js/src/plugin/client.js
index 2f34c4e..6d55d25 100644
--- a/dev/js/src/plugin/client.js
+++ b/dev/js/src/plugin/client.js
@@ -23,11 +23,11 @@
  * demand using integrity check:
  * https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
  */
+"use strict";
 
-var cs = document.currentScript;
+const cs = document.currentScript;
 
 (function () {
-  "use strict";
 
   // Similar to randomID in server, but a bit cheaper
   function randomID () {
diff --git a/dev/js/src/plugin/server.js b/dev/js/src/plugin/server.js
index 96b5cb7..19f8c5f 100644
--- a/dev/js/src/plugin/server.js
+++ b/dev/js/src/plugin/server.js
@@ -7,9 +7,9 @@
  *
  * @author Nils Diewald
  */
+"use strict";
 
 define(['plugin/widget', 'plugin/service', 'state', 'util'], function (widgetClass, serviceClass, stateClass) {
-  "use strict";
 
   KorAP.Panel = KorAP.Panel || {};
 
diff --git a/dev/js/src/plugin/service.js b/dev/js/src/plugin/service.js
index 3a39c4d..a76b2e4 100644
--- a/dev/js/src/plugin/service.js
+++ b/dev/js/src/plugin/service.js
@@ -1,5 +1,6 @@
+"use strict";
+
 define(function () {
-  "use strict";
 
   // Limit the supported sandbox permissions, especially
   // to disallow 'same-origin'.
diff --git a/dev/js/src/plugin/widget.js b/dev/js/src/plugin/widget.js
index 546cd1b..5f8ca9a 100644
--- a/dev/js/src/plugin/widget.js
+++ b/dev/js/src/plugin/widget.js
@@ -7,9 +7,9 @@
  *
  * @author Nils Diewald
  */
+"use strict";
 
 define(["view","plugin/service","util"], function (viewClass, serviceClass) {
-  "use strict";
 
   return {