Fix SharedBatchWriter and increase findbugs level

In #59, Findbugs was added. It found a bug in the SharedBatchWriter where a static field (exportQueue) is being written to in an instance method (SharedBatchWriter constructor). After this is fixed, the find bugs level should be raised by removing the property findbugs.maxRank from the fluo-recipes parent pom.xml.

Start at the SharedBatchWriter constructor, where exportQueue is written, and inspect the parent pom.xml property findbugs.maxRank. Done means the static-field write is corrected and removing that property raises the FindBugs level without introducing new findings.

Written by the indexing model from the issue text.