[Qgis-developer] [WIP] Multiple geometry column support and new geometry editor widget

[Nyall Dawson]

Announcing work-in-progress regarding adding support for handling
multiple geometry columns from providers (ie, keeping the additional
geometry columns as proper QgsGeometry objects rather then converting
them to strings).

A part of this work also involves creation of a new "geometry editing
widget" used as a delegate for additional geometry columns in the
attribute table. The widget allows for copy/pasting the geometry
attached to a feature in a variety of formats (wkt and geojson), and
for clearing the geometry attached to a row.

It's in early experimental stages (just a fun hack for me for now),
but please contact me if you are planning related work!

Nyall