Refresh styles

It is time to change the wallpaper:

• update icons: some are old, some are unnecessary, some are confusing
• change default button styles
• style intro and helpers paragraphs in order to unify the styles of these types of messages
• update global styles to change the default GWT skin to something a bit lighter
• Tabs style
• Search layout tables in COntent views
• titles (information architecture)
• Highlight style (on left tree selected item)
• [?] Help style (just ? would be possible?)