This adds the ability to select multiple devices either by a ctrl-mouse drag
or by ctrl-click on individual devices title to do finer selection
and deselection, and then ctrl-right-click on the canvas to produce a menu
with the options to cut/copy/paste/delete selection or to merge an existing
patch entirely into the patch. Pasting or merging will auto-select new devices
so any old devices will lose selection.

To remove selection simply click anywhere on canvas.

Current problems -

Multiple Select drag is buggy and may select items not in the selection area.

Multiple OSS plugins are buggy so merging/pasting an OSS device can cause crashing.