rqt_reconfigure: Update maintainer
rqt_reconfigure: Cache received param changes

rqt_reconfigure: Unify update value naming

Currently, the 'old value' is cached when we send changes (so we don't send an unnecessary update). When the value is changed externally, however, we should update the 'old value' to prevent unnecessary updates here, too.
rqt_reconfigure: Clean up console messages
rqt_reconfigure: Improve checkbox behavior
rqt_reconfigure: Use signals to trigger GUI updates