Features/1268 json crash

This should fix #1268 and fix our OOM errors.

I believe this was caused by some bad error checking on out of storage.  This patch will ensure that we don't grow without bound, but it doesn't do anything to clean up storage if we run out of diskspace.

This puts a hard limit on the number of StumblerBundle instances that can be inside of a single ReportBatchBuilder instance.

Tests added checking the underlying StumblerBundle and string lengths are in ReporterTest, while checks against the total number of StumblerBundle instances are contained in DataStorageManagerTest.