Third fixup release for Turris OS 5.1

• It makes factory reset on Turris Shield easier as long-pressing RESET button does factory reset.
• Fixed issue when CA for OpenVPN was not created in some cases
• BIND: DNS Flag Day 2020
• Updated reForis (fixed WebSockets)
• Dropped Transmission variants (openssl, mbedtls)

Misc: Updated Python to 3.7.9