Improving "erase scenes" feature and filtering feature

[tatt61880]

(4): Implemented at v1.7.5.
(1), (2), (3): Not implemented yet.
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* About "erasing scenes" feature.
(1) Making subfolders in "scenes/trash".

Added ability to erase scenes in the "Load scene" menu.

It is cool feature that erased scenes will be moved into "scenes/trash" folder.
However, the "trash" folder becomes jumble if trash folder doesn't make subfolder.
So I suggest that moving scenes in subfolder of "trash" when you erased scenes which in subfolder of "scenes".
(ex. when you delete "scenes/car/myCar.phz", move the scene into "scenes/trash/car/").

(2) Add ability to erasing folders.

* About filtering scenes feature.
(3) Improve the filter feature of loading scenes.
When you input "lessons" into filter, it shows the "lessons/" folder. However, when you input "lessons/" into filter, it doesn't show "lessons/" folder.
I consider it is not proper filtering for users.

(4) After showing subfolders, input cursor had better in filter textbox.
(ex. inputing "Ctrl-O", "tab", "tab", "space" shows ".." folder. After that, you have to use mouse for inputing something into filter-textbox.)

[tatt61880]

4 is once implemented, but 1.9.x behaves not so.