Feature autosubpatching. First stage.

Add autosubpatching feature for a set of selected objects. First stage: add new canvas method "subpatch", add new copy method that creates xlets in addition to current functionality, add subcanvas creation, add selected objects copy and clear, add cut objects paste and displace into newly created subcanvas.

Note1: probably subcanvas creation process has to be replaced with pd messages but we need the subcanvas reference to be able to paste the objects into it, and for now is the only way I have found without having to follow the 'garray_init' method (hardcoded subcanvas creation, do stuff and send a pop message) Note2: some placement magic numbers have to disappear