peers had combined meaning, both being referenced by history for which
chat a message was in, and being reference by aliases for who authored a
message. This means that peers had conceptually different sub-groups:
all friends are both a chat and an author, but self is an author but not
a chat. With the addition of group chats this is amplified by groups
themselves being chats but not authors, and group members being authors
but not chats. Instead of having four sub-groups all within peers,
splitting peers into chats and authors gives a clean mapping,
simplifying interactions with the data.
In the new chats and authors tables, store what used to be a public_key
string as a BLOB, since it’s inherently a 32-byte binary value in both
cases. Call the public_key a UUID for chats, since group IDs are not
defined as public keys by toxcore.
Even though the data change is quite minor, the upgrade is large because
of SQLite's lack of support for modifying foreign key constrains for
existing tables. This means when peers are moved to new tables, all
tables referencing peers need to be cloned with a new foreign key
constraint, as well as all tables referencing those, recursively.
