Common interface for SevenZFile and ArchiveInputStream

Both SevenZFile and ArchiveInputStream (effectively) have a method on them:

ArchiveEntry getNextEntry()

However, they don't share a common interface or parent which defines this, so it isn't possible to write generic code which would work with either to read archive entries out

For Apache Tika, it would be good if after our 7z specific opening code, we could then use common code to read out and process the archive entries no matter what the archive format was