Use platform native file browser instead of tkinter.filedialog

[modalexii]

Currently file and directory selection is handled via the filedialog class, which is serviceable and portable but offers a degraded experience (IMO) from the OS native file browser. As an example, on Windows I keep my sketches at a location similar to: E:\shared_home\Documents\Git\<git username>\<get repo>\, but also have the examples and other code within some default and/or sensible locations on C:\. Switching back and forth between the two locations in the current dialog requires clicking This PC and navigating down from the drive root. Invoking explorer.exe (or xdg-open in Linux, or the OSX equivalent, etc) would allow me to browse much faster via the side panel's Quick Access links or tree view, or whatever analogous customizations users have set up on other operating systems.

Granted this increases fragility when supporting as many platforms as possible, but it's a solvable problem.