Icons not properly unregistered

[Former user]

Hi, Thank you for this great addition !

Found a small unregister issue: the addon dosent properly unregister icons.

ResourceWarning: <ImagePreviewCollection id=0x1e3e9a73278[0]>: left open, remove with 'bpy.utils.previews.remove()'

Should add something like this in ui_utils and call from unregister:

for icons in preview_icons.values():
        bpy.utils.previews.remove(icons)
    preview_icons.clear()

[renderhjs]

I believe this has been addressed here https://bitbucket.org/renderhjs/textools-blender/commits/c72e2278121da78164fbd3bd8dfb5236a326053f and I believe does not happen anymore in version 1.1.0