refactor(webinst): Remove <changelog> node in info.xml (refs #4385)

The use of the <changelog/> node is deprecated, and replaced by a
"changelog" property (on the <module/> node) which contains a URL to the
changelog.
Merge pull request #26 from eguaj/2.0-A4385

refactor(webinst): Remove <changelog> node in info.xml (closes #4385)