Fix auto-check issues after successful connection attempt

• immediately after receiving the connected signal appearantly we cannot write to the VPN, only after a small delay. I couldn't find a better solution for now than implementing exactly that delay, but if I find time for it at some point I should figure out the root cause.
• this workaround fixes the checks for new app updates, certificate updates and eip-service.json updates after a successful vpn connection attempt
• it also fixes a notification sound bug on pre android 8 devices when the app tries to download a new app version (that feature only in web-downloaded versions available)
• minor cleanups

closes #9093 (closed)