Implement queryOne routine in DBHandler.

Add a new routine DBHandler::queryOne, that returns a full QSqlRecord as
result, so that multiple fields can be read from it at once.
Implement name_update calls.

Perform correct name_update calls to send credential-hash-names to the
Nym's source address, as well as setting their value to the correct
signature message.
.gitignore Qt-generated Makefiles.