doc: updated it.po
adg: dependency between AdgStroke and its model

Keep a reference of the underlying model inside AdgStroke.

Closes issue #99: http://dev.entidi.com/p/adg/issues/99/
doc: updated TODO.xml
demo: corrected metadata valign in adg-demo.ui

Removed useless parent GtkVBox to pack the metadata frame on top of the
notebook container.
doc: updated NEWS.xml
adg: invalidate "scale" text directly in AdgCanvas

Handle the "scale" invalidation directly in the local-changed default
handler of AdgCanvas. Removed scale settings from adg-demo.
doc: updated it.po
build: bumped version to 0.7.2