XML format for property updates report

[KTannenberg]

XML format was introduced for plugin and dependency update reports in #112/#93.

However it is rather common and convenient to specify version as a property especially when you a working several dependencies of same version (e.g. in pretty much any Spring application).

Goal versions:property-updates-report should allow to specify report format(s) similar to versions:dependency-updates-report and versions:plugin-updates-report.

[maxime-michel]

This is just great, any reason you didn't create a PR with your changes?

[KTannenberg]

@maxime-michel, I simply forgot about it :)

Here's PR: #554