1. default-config param in config .yml for thumbnail does not do anything - thumbnail icons do not change for new or old ContentTypes
2. Setting thumbnail using direct .svg icon path will not display icon anywhere
3. Editing single Content (content/location/5) will not show icon even if it's still visible in a tree or ContentType editor

Steps to reproduce:
1. Create new ContentType of name "House" and identifier "house" with ezstring field (or any).
2. Create a new Content for this ContentType i.e. "House1".
3. Edit .yml config file as shown in https://doc.ezplatform.com/en/latest/guide/extending/extending_back_office/

system:
    default:
        content_type:
            default-config:
                thumbnail: "/bundles/ezplatformadminui/img/ez-icons.svg#collection"

4. Try to change the icon directly:

            house:
                thumbnail: "/bundles/ezplatformadminui/img/icons/collection.svg"

Results
After 2nd "Step to reproduce" the file icon is visible in the tree but not in a Content View on the right side.
After 3rd "Step to reproduce" new icon is not visible in Content View or in a Content Structure or in Content Type list.
After 4th "Step to reproduce" icon is not visible in Content View or in a Content Structure or in Content Type list.

Expected Result
After 2nd "Step to reproduce" file icon will be visible in the tree but should be visible in a Content View on the right side as well (file icon should be visible before "House1").
After 3rd "Step to reproduce" new icon should be visible in Content View or in a Content Structure or in Content Type list.
After 4th "Step to reproduce" new icon should be visible in Content View or in a Content Structure or in Content Type list.