Match Confluence behavior for link anchors

When creating an explicit anchor in Confluence, the actual id is not directly whatever the user has typed:

• in Confluence server, spaces are removed and the page title without space is prepended

• in Confluence cloud, two A HTML tags are produced:

• • one where spaces are converted to dashes
  • one where, in addition to the former, the page title is prepended, with spaces converted to dash.

We shall:

• convert anchors with this in mind
• provide an option to specify which kind of instance was used to create the imported backups, since anchor behavior depends on this
• autodetect the kind of instance whenever possible. The exportDescriptor.properties has a "source=cloud" line when exporting from cloud, so we will assume "cloud" when this is present, "server" when this is absent. Newer versions of Confluence server seem to have source=server as well.