This reduces the attack surface for data that can come from
malicious sources (exported output and key images, multisig
transactions...) since the monero serialization is already
exposed to the outside, and the boost lib we were using had
a few known crashers.
For interoperability, a new load-deprecated-formats wallet
setting is added (off by default). This allows loading boost
format data if there is no alternative. It will likely go
at some point, along with the ability to load those.
Notably, the peer lists file still uses the boost serialization
code, as the data it stores is define in epee, while the new
serialization code is in monero, and migrating it was fairly
hairy. Since this file is local and not obtained from anyone
else, the marginal risk is minimal, but it could be migrated
later if needed.
Some tests and tools also do, this will stay as is for now.
