Processor for page revisions in XML dumps

[mkroetzsch]

A component for processing the page revisions found in one or more dump files in MediaWiki XML format should be provided. The component should process a file given by a Java file handler (no path!) and iterate over the revisions in that file. Other components that process revisions should be able to register as listeners, which will be called back for every new revision. The iterator should also be able to parse multiple files (last dump + incremental daily dumps), obtained from the dump file management component of Issue #8.