Unifications and a few smoother icons, compatible with My Little Forum 2.4.20

Changes

• the padlock bodies of the lock/unlock icons got colour gradients, that replaced the previous used three planes construction
• the HTML-structure and CSS-rulesets of the functional links (edit, delete, change order) in the tables of the pages for user administration, categories, smilies, additional pages (admin area) and the list of own bookmarks got unified
• within this procedure the link texts got masked so only the icons are visible, this was done in a way that the masked texts are still reachable for screen readers and text only browsers (for example search bots)
• a bit of padding for the table cells in the mobile view (display: block; for narrow viewports like smartphone displays in portrait modus)