[types] impl conversions from/to prost proto and EventProof
[types] impl conversions from/to prost proto and EventProof

Closes: #1188
Approved by: andll

aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,libra/libra,libra/libra,aptos-labs/aptos-core