Use 'sugar' icons and no 'gnome' icons.

Right now IconTheme return the icons of the gnome theme,
with this patch, its compare the paths..

If the icons contain some text of the normal sugar icons path,
its uses it. (/icons/sugar/)

Before this patch, the journal show gnome icons in mime_types

Fixes SL#4791
Use the bundle registry in sugar-install-bundle; fixes #4722

The bundle registry properly signals the activity list to update its entries,
whereas directly installing the bundle does not emit any signals (unless it is
an install or uninstall).
Fix unicode escapes in clipboard objects

It returns the UTF-8 text to the clipboard to show in the preview,
instead of the HTML formatted one.

Fixes SL#3930