Release iText 5.5.4

Release of iText 5.5.4 Core on December 17, exactly 3 months after the previous release. If you have a look at the changelog, you'll notice that XFA Worker has received a lot of attention in this release. 

Our initial XFA customers are very happy with the functionality we provided in previous versions, but new XFA customers are discovering more and more features in the XFA spec and we're consistently adding these features to XFA worker.