PLT-3408 Add SiteURL to config.json (#3692)

* PLT-3408 Changed serverside code to get the service's URL from config.json

* PLT-3408 Changed most clientside code to use the SiteURL config setting instead of window.location

* PLT-3408 Changed default SiteURL to be autodetected

webapp/components/file_attachment.jsx

@@ -102,7 +102,7 @@ class FileAttachment extends React.Component {
     getFileInfoFromName(name) {
         var fileInfo = utils.splitFileLocation(name);
 
-        fileInfo.path = utils.getWindowLocationOrigin() + Client.getFilesRoute() + '/get' + fileInfo.path;
+        fileInfo.path = Client.getFilesRoute() + '/get' + fileInfo.path;
 
         return fileInfo;
     }