Keep class properties closed when default in custom properties that are classes.

[smjnab]

Is your feature request related to a problem? Please describe.
If using custom properties that are classes, currently they are always fully shown in Tiled. You can click the small arrows to close the class and the subclass properties, but each time you go back to an object, they will have been re-opened. This can take up quite a lot of screen space, making scrolling or a constant closing of properties a cumbersome task.

Describe the solution you'd like
That classes/sub-classes remain closed when they do not have any values edited that differ from the default (as in when they get the bold text).

How it is now:

How it would be: