Various fixes

[egbertbouman]

This PR:

• Updates the downloads table to prevent line breaks.
• Fixes add_ffa_from_dict to update tracker_info when needed.
• Updates TriblerTunnelCommunity.on_raw_data to show additional debug info.
• Removes HTTP logic from TriblerTunnelCommunity. This functionality is now part of ipv8-rust-tunnels.
• Fixes endpoint.get_address always returning an empty address.
• Introduces the notation of backup exit nodes. Backup exit nodes will only be used if regular exit nodes can't be found.
• Limits the number of introduction points.
• Imrpoves TriblerTunnelCommunity peer discovery.

[egbertbouman]

validate

[teddyrogers]

@egbertbouman @qstokkink any chance of a new build with current fixes please?