Multiple SQL statements should be in deferred transactions

[bbappserver]

SQLITE must always open a transaction to change the database and this has overhead. Items in https://github.com/bbappserver/hydrus-userpatch/blob/develop/include/ClientDB.py would be faster if successive executes were wrapped in BEGIN. As a transaction would not have to be opened and closed every time. Don't worry, SQLITE already deals with read concurrency.