configconvert: notification_options -> notification_{state,type}_filter

parsing the existing comma separated list and using some perl hash magic
to convert it to the new notification_type_filter and
notification_state_filter logic.

fixed missing file permission check on writing config files too.

fixes #4060
configconvert: disable some debug leftovers

$ find -type f -name '*.pm' | xargs sed -i 's/[^#]say Dumper/ #say
Dumper/g'
configconvert: skip empty notification filters

refs #4060
configconvert: fix 'n' and 'a' notification_options (filter = 0, filter = ...)

refs #4060
configconvert: treat 'null' (disable inheritance) as '0' instead

refs #2743
configconvert: update README (NOTES and TODO)

refs #2743
configconvert: custom attr (CVs, *_url, notes, *image*, 2d_coords)

collect attributes
* notes
* icon_image
* icon_image_alt
* action_url
* notes_url
* statusmap_image
* 2d_coords
* _CVs
* !__I2CONVERT

and stash it onto the custom dictionary.

note: attribute names starting with a number need to be quoted.

fixes #3096
configconvert: update README

refs #2743
Merge remote-tracking branch 'icinga2/master'