Ensure ExoneraTorDatabaseImporter closes all BufferedReader/Writer objects

If Exceptions occur in ExoneraTorDatabaseImporter's readImportHistoryToMemory() and writeImportHistoryToDisk(), the BufferedReader/Writer object they each use may not be closed.

A proposed solution can be seen at

git@gitlab.com:743zpnpGUq27GgR/exonerator.git 

in the branch "close-open-bufferedreaders".

Trac:
Username: efgyirfe784