Protobuf Panics for GG20 Branch

[daryakaviani]

I believe this the fix at #106 needs to be integrated into the GG20 branch as well. While it was just a warning before, protobuf has been updated to panic on name registration conflicts. GG18 on the main branch works fine for me, but using my code with the GG20 branch gives:

panic: proto: message KGRound1Message is already registered
See https://developers.google.com/protocol-buffers/docs/reference/go/faq#namespace-conflict

Does the GG20 branch need to be updated to accommodate this protobuf change, i.e. does this mean GG20 is permanently broken until this fix is made? Alternatively, is there another workaround I can use to simply run GG20?

CC @lukasz-zimnoch @omershlo @Shadowfiend @PlamenHristov @yycen