Use SVG image for WebUI favicon

This will allow browsers to get high quality icon with required
resolution instead of resizing some small raster image.
Browsers can have even more benefit from it. For example, Firefox uses
high resolution icon to display it in "Top Sites" instead of page
preview.

Nothing changes for browsers which doesn't support SVG favicons, older
PNG icon will be used in such case.

src/webui/www/private/index.html

@@ -6,6 +6,7 @@
     <meta http-equiv="X-UA-Compatible" content="IE=10" />
     <title>qBittorrent Web UI</title>
     <link rel="icon" type="image/png" href="images/skin/qbittorrent32.png" />
+    <link rel="icon" type="image/svg+xml" href="images/skin/qbittorrent-tray.svg" />
     <link rel="stylesheet" type="text/css" href="css/dynamicTable.css?v=${CACHEID}" />
     <link rel="stylesheet" type="text/css" href="css/style.css?v=${CACHEID}" />
     <!--<link rel="stylesheet" type="text/css" href="css/Content.css" />-->

src/webui/www/public/index.html

@@ -5,6 +5,7 @@
     <meta charset="UTF-8" />
     <title>qBittorrent QBT_TR(Web UI)QBT_TR[CONTEXT=OptionsDialog]</title>
     <link rel="icon" type="image/png" href="images/skin/qbittorrent32.png" />
+    <link rel="icon" type="image/svg+xml" href="images/skin/qbittorrent-tray.svg" />
     <link rel="stylesheet" type="text/css" href="css/login.css?v=${CACHEID}" />
     <noscript>
         <link rel="stylesheet" type="text/css" href="css/noscript.css?v=${CACHEID}" />