Some case of unwanted settings folders creation : When calling settings paths from SettingsModel, we checked on default in all cases. That lead to create folders to be writable.
=> Check for default only if path has not been overwritten in linphonerc.
Replace black thumbnails that contains transparency by white color.
Thumbnails are in jpg where there is no transparency. By default, transparency is replaced by black color because not background color has been defined.
=> Set background image in white.
