refactor(webinst): Remove <changelog> node in info.xml (refs #4378)

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 #13 from eguaj/0.4-A4378

refactor(webinst): Remove <changelog> node in info.xml (closes #4378)