Improvements to JarArchive / WarArchive

Currently the JarArchive / DefaultJarArchive only provides a read-only access.

It would be nice to have functionality to be able to modify (add/remove/change) the files within a Jar archive, explode the JAR into a directory, etc.

I don't know whether this should be in the interface (JarArchive), or only in the implementation (DefaultJarArchive).

Also, the current implementation stores the Jar (or war, etc) content as a member variable (private byte[] content). This means that if the archive is large it eats a lot of memory - it could (in findResource) create a JarInputStream from the File that it was passed originally.