Sketchbook subfolders not supported

[ubidefeo]

Describe the bug
The Java IDE's File > Sketchbook menu is structured according to the folder structure of the sketchbook folder. Sketches in subfolders of the sketchbook are shown in submenus of the File > Sketchbook menu. This is very useful for organization once you accumulate a lot of sketches.

So given this sketchbook structure:

{sketchbook folder}
|_ Bar
|    |_ Bar.ino
|_ Foo
|    |_ Foo.ino
|_ sketchbook-subfolder
    |_ Baz
         |_ Baz.ino

The Java IDE's File > Sketchbook menu looks like this

IDE 2 currently only recognizes sketches in the root of the sketchbook folder, so given the above sketchbook folder structure, the menu looks like this:

Desktop (please complete the following information):

• OS: Windows 10
• Version: 2.0.0-beta.2-snapshot.298cc11
• CLI Version: 0.16.0 alpha [c977a238

Additional context
Sketches in the libraries and hardware subfolders of the sketchbook folder are not affected.

[ originally reported by @per1234 ]

[kittaakos]

Closed via #198.