Gossip and other places repeatedly de-serialize vote-state stored in
vote accounts. Ideally the first de-serialization should cache the
result.
This commit adds new VoteAccount type which lazily de-serializes
VoteState from Account data and caches the result internally.
Serialize and Deserialize traits are manually implemented to match
existing code. So, despite changes to frozen_abi, this commit should be
backward compatible.
behzad nouri