[useradmin] add "shared links" tab
[sysadmin] Refactor share links in user info page
[share link] added 'expiration' back
[repo_settings] added 'shared links' back
Add 2 email settings to share link sending
* REPLACE_FROM_EMAIL - replace email from field to username
* ADD_REPLY_TO_HEADER - add Reply-to header
[lib setting] improved ui of 'shared links'
[lib setting] improved code indention
[repo-setting] fix bug while checking download/upload links
[sys-admin] at user-info page, remove shared links if related
            dir/file has already been deleted
[sys-admin-traffic] add hyperlink to username
[org] use 'Settings' as tab name
[org] use 'Settings' as tab name at other pages
[fileupload] added 'add folder'
[thumbnail] Show image file's thumbnail
[thumbnail] show image file's preview
[thumnail] use css to center the preview img