Move registering WebUI magnet handler behind toolbar option

Alert the user if the operation fails due to lack of browser support

src/webui/www/private/index.html

@@ -77,6 +77,7 @@
                         <a class="returnFalse">QBT_TR(Tools)QBT_TR[CONTEXT=MainWindow]</a>
                         <ul>
                             <li><a id="preferencesLink"><img class="MyMenuIcon" src="images/qbt-theme/configure.svg" alt="QBT_TR(Options...)QBT_TR[CONTEXT=MainWindow]" width="16" height="16"/>QBT_TR(Options...)QBT_TR[CONTEXT=MainWindow]</a></li>
+                            <li><a id="registerMagnetHandlerLink"><img class="MyMenuIcon" src="images/qbt-theme/kt-magnet.svg" alt="QBT_TR(Register to handle magnet links...)QBT_TR[CONTEXT=HttpServer]" width="16" height="16"/>QBT_TR(Register to handle magnet links...)QBT_TR[CONTEXT=HttpServer]</a></li>
                         </ul>
                     </li>
                     <li>

src/webui/www/private/scripts/client.js

@@ -590,6 +590,10 @@ window.addEvent('load', function() {
         MochaUI.Desktop.setDesktopSize();
     });
 
+    $('registerMagnetHandlerLink').addEvent('click', function(e) {
+        registerMagnetHandler();
+    });
+
     $('speedInBrowserTitleBarLink').addEvent('click', function(e) {
         speedInTitle = !speedInTitle;
         localStorage.setItem('speed_in_browser_title_bar', speedInTitle.toString());
@@ -801,13 +805,13 @@ window.addEvent('load', function() {
         addMainWindowTabsEventListener();
         addSearchPanel();
     }
-
-    registerMagnetHandler();
 });
 
 function registerMagnetHandler() {
-    if (typeof navigator.registerProtocolHandler !== 'function')
+    if (typeof navigator.registerProtocolHandler !== 'function') {
+        alert("Your browser does not support this feature");
         return;
+    }
 
     const hashParams = getHashParamsFromUrl();
     hashParams.download = '';