Add option to choose from existing cross section definition

[Patrick-Nijman]

"There's no possibility to choose an already existing cross section definition. Now every time a pipe is added a new cross section is made, while this is not necessary" [Rebecca]

We will probably need some search/filter functionality to find the cross section definition you need. Some models have many of them.

[leendertvanwolfswinkel]

Never heard anyone request this since we removed the option in the geopackage database schema, closing the issue