from pd-l2ork: f3c4044dc6a28185488f365be8a6ebd61fba6315

*patch to add [group] data structure and supporting fixes (work in progress with lingering bug of being unable to display data structure arrays properly, see tiger.pd demo patch in data structures)

*fixed incorrect getrect when selecting a plot with scalars at each point (see setsize-help.pd). This was a regression from an earlier "fix" (see https://github.com/pd-l2ork/pd/commit/f0916f85a11894a43067d5b07ae5f8eea2b2c1b9#diff-5ff2b78bd60b3b9c36db43b8d5f5c168). The latest code does not exhibit the said problem so this should be all ok.
*fixed embedded scalars at each plot point not being selected for displacement with tag due to clumsy way of labeling them. This is achieved by adding scalar arg to the parentvisfn which also alters g_canvas.h spec but also makes things more streamlined.