refactor(webinst): Remove <changelog> node in info.xml (refs #4371)

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 #23 from eguaj/1.0-A4371

refactor(webinst): Remove <changelog> node in info.xml (closes #4371)