port c6771297b6f03887034c5f121d3dbf701623ab87 from Pd-l2ork: the big Vanilla forward port won't compile without this commit

got a very early working version that does _all_ object text editing (arrow keys, selection, etc.) in the GUI. (However, it still depends on g_rtext.c for doing everything else.)

*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)

- nested plots display properly
- plot is vis'd and unvis'd properly when deleting plot or struct
- commented out ugly plot_displace hack-- multiple plots should work just fine
- separated out garray dependencies into class "old_plot".  This way the changes I made don't affect garrays.  _Very_ ugly hack, but it was pretty simple to implement and will be easy to remove later.
- no crashes when non-existent arrays are entered into a [struct] that has scalars hanging around
- template_cancreate ported from 0.45
- added a function to get the offending struct (to use with "Find last error").  Not using it yet, though.
+ For creating scalars using an object box:
- scalar must have initial "float x float y" fields, in that order.  This means you can't accidentally type the name of the hidden garray structs and create a scalar.  (Nor any other structs that only have a "y" field, etc.)
- broken object box returned if the struct has a bogus array template.  (Although currently I'm just refusing to create such a struct.)

*cannot create two structs on the same canvas (otherwise how would you know which one you are talking to)?
*fixed regression where arbitrary font sizes were not honored by the drawsymbols and drawnumbers
*other minor clean-ups
*adjusted help file to reflect the new approach to font sizes

*fixed bug where with JOC enabled in subpatch this only works for the bbox of the array, not the entire window
*made intelligent offset to various forms of array representations so that scrubbing with mouse accurately applies to closest points
*disabled drawing of a GOP rectangle inside GOP array window
*disabled ability to insert objects inside a subpatch with an array

added Jonathan's revision of the array properties and options with fixed font sizes and other minor fixes. LINGERING PROBLEM: array does not redraw (only after apply does it re-appear). Likely shouldvis problem.

*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.

*better getrect for scalars inside plot/array (entire points are now selectable instead of arbitrary rectangle around the object)

forgot to include another file and additional improvements to the previous commit, including improved tofront/back behavior (apart from lingering bugs)

*stretchable objects (like 0.45) with undo/redo capability, diagonal resize cursor, and minimum gop size.

revamped path to support ~/, root paths, relative paths, as well as special tags like @pd_extra that expands to the location of the extra folder (other tags may be added later if necessary).

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

improved nlet highlighting (integrated it into glist), fixed bug with multiselect with mixed objects (accelerated and legacy)