[UX] streams component should show a warning if offline

[Ivshti]

if the user is offline, the streams component should show a warning along with the available streams

if all add-ons are accessed through network, the usual message will be "no streams available" as there will be no responses; in this case it will be "no streams available; warning: you're offline"

it's important that this warning shows alongside the component cause there may still be streams available from the local add-ons