notification_create currently simply allocates memory and zeroes it to
properly initialise a notification. Since we currently have at least 2
places in the code that create notifications(startup notification in
dunst.c and notifications from dbus in dbus.c) the creation should be
handled from a central location in case we ever need to change the
creation procedure later on.
Expand the duplication checking functionality to also check for urgency
and icons. If icons are turned off in the settings the icon check is
skipped.
Icons matching is done based on the given path, if the path differs or
an icon name is used for one notification but an absolute path for
another, the icons are considered different even if they refer to the
same file.
