WIP: set up GUI <-> Pd interface for turning off scrollbars and menus

This adds options to the Canvas Properties dialog for turning off scrolling and disabling the menus.

Currently this only adds the checkboxes to the menu, sets t_glist state, and saves the settings to a patch file.

If they are enabled, then no state is saved to the patchfile so that it remains backwards compatible.

If menu is disabled, an #X menu 0 message is added to the patchfile in the same relative location as the #X coords message currently does.

If scrollbars are disabled, an #X scroll 0 message is added as well.

This is the easiest way to implement these features, at the expense of generating two potential error messages when opening Purr Data patches in Pd Vanilla.

An alternative possibility would be to have a single #X visual message with additional args to define the visual aspects. In this case, something like #X visual menu 0 scroll 0. But that's more difficult to parse and more difficult to deal with multiple sub-arguments.