gui: Throttle GUI update pace when -reindex
gui: Throttle GUI update pace when -reindex

Co-authored-by: Barry Deeney <mxaddict@codedmaster.com>
Co-authored-by: Russell Yanofsky <russ@yanofsky.org>

Former-commit-id: b005c017039119b4bb1c7371265db8d0787a02c5
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin