Memory issues while performing LevelDB batch write

[RCasatta]

In my server memory usage spikes here

opentimestamps-server/otsserver/calendar.py

Line 205 in ac67218

self.db.Write(batch, sync=True)

I was wondering if we should write batch incrementally, for example after this log call

opentimestamps-server/otsserver/calendar.py

Line 200 in ac67218

logging.debug("Added %d timestamps to LevelDB; %f stamps/second" %