The daisydiff library isn't usable in standalone mode

See https://github.com/DaisyDiff/DaisyDiff/issues/2

Problem is that the jar built by Maven doesn't embed the org.cyberneko:html and xerces:xercesImpl dependencies. Yet they are part of a Nuxeo distribution which allows the nuxeo-diff addon to work well.

We should probably provide a standalone profile to generate a jar with the -standalone qualifier embedding both libraries.