refactoring of the mappings package: Renames Extractor to PageNodeExtractor and Mapping to Extractor
Merge pull request #141 from jimkont/extractors

refactoring of the mappings package
Fix HomepageExtractor issues

The HomepageExtractor was not able to correctly detect references to official webpages
when conveyed through templates placed in the External links section.
Only matches to Template:Official were considered and the URL extraction was failing
when the template property contained an ExternalLinkNode.

With this change:
- A map is provided to store info about official website templates, for different langs
- Template redirects are checked when looking for official websites
- URL is extracted also when the template property is an ExternalLinkNode

I was able to extract 550k homepages from enwiki-20130604 compared to about 505k items
without this patch (about 10% more).
Merge pull request #126 from ninniuz/homepage_extractor_fixes

Fix HomepageExtractor issues
Issue #144: Deduplicate quads in the extraction server

When extracting quads from the extraction server, we should
deduplicate quads so that we get a similar result to that
produced by the extraction framework
Merge pull request #146 from ninniuz/144_duplicate_quads

Issue #144: Deduplicate quads in the extraction server
manually merge pull request #95 / fixxes issue #23
bugfix provided by @ninniuz