fix invalid finality proof

[haerdib]

Changes copied from https://github.com/integritee-network/worker/commit/1a06fa456328d442ea3ce551ee7edbb820950dff:

• removal of communication block (speficially functions localized_payload_with_buffer and check_message_sig_with_buffer) because they are now implemented in the sp_finality_grandpa crate which implements no_std.
• adaptions (mostly copy paste) according to substrate sc-finality-grandpa justifications.rs
• chain relay will not panic upon faulty justification but print an error message

closes #229