All MediaDownloadTask items are created from the same thread

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Remove unneeded thread

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Improve network access manager handling

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>