doc: updated docblock license
Refactored dimensions in piston.lua

Dimensions are not a model: moved into the view section and stripped
from the model table.
Moved title block code on its own

Created a dedicated function to set the title code: a lot of data will
be shared between different views, so no need to duplicate it.
adg-demo: added bare editing capabilities

Handling the edit dialog and updating the drawing on request. There are
still some rough edges but the program is almost equivalent (but a lot
shorter and neater) to the original adg-demo.c.