We have WebXmlMerger which merges WebXml files (web.xml and whatever container-specific descriptors exist).
Provide WarArchiveMerger, which has the same interface (=used in the same way) that WebXmlMerger is.
Is constructed with the relevant WebXmlMergers, and Document mergers (CARGO-257). When executed all the merging takes
place, and the resultant War file can then be saved to the filesystem.