added preset_node_array abstraction and supporting help files (plus improvements to preset_node and preset_hub)

fixed elusive problem with undo where actions did not behave properly because of failing to update canvas_undo_name

all gop widgets (at least ones in vanilla release) have their nlets hidden when displayed inside GOP, as having them is entirely superfluous in that view

fixed image external to conform with the new implementation of @pd_extra (and later other possible sys args) of the file path parser

streamlined @pd_extra parsing for easier integration with other file open calls including externals. Added it to open_via_path

added pdtk_canvas_force_getscroll function to ensure critical getscroll events are executed immediately

optimizations to the scrolling algorithm including erroneous jumps in the scrollbar when pasting/cutting/duplicating things.

streamlined selection logic and added ability for pd to recognize system-wide @pd_extra variable within the path

finished importing the remainder of new K12 module abstractions, updated GUI to reflect them, improved key press capture, reformatted GUI object menu inside K12 mode to allow for more space