[Persistence] Specify last modified (derby compatibility)

Apache Derby does not support
ON UPDATE CURRENT_TIMESTAMP, which is used
in prior commits to match modified time to
that read from database. As an alternative,
use time read from database during polling
to estimate the current database time when
persisting components (adjusting for the
local time elapsed since the database time
was last read.)
[Persistence] Poll broader range of time stamps

Look back one extra polling interval when
checking for updated last-modified times.
These are estimated by the client and may
not reflect precise database CURRENT_TIME
at the time of commit, whereas polling
does use precise CURRENT_TIME. This may
result in redundant updates but should
avoid missed updates, except in cases of
extreme latency.