[Backport] In the sitemap tree, show page title in tool tip

Requirements:

On hover over a leaf item in the sitemap tree, show a tool tip:

• that displays the document name for xpages
• that displays the page title for hst pages (landing pages) if available,
• for hst pages without a page title, show the URL name (same as in the tree)

Rationale

In the list view of the site map, both page title and URL were displayed. In the new hierarchical view, only the URL name is displayed. It would be nice to include the page title in the tree somehow. 

As it is based on the page title by default, we assume that users can recognise the page title in the URL name. The page title therefore wouldn't have to be visible always, and showing it in a tool tip would be enough. But this needs to be verified

Customer feedback

When editing a site in a different language (e.g. Russian) it is impossible to distinguish which page an editor is looking at since they don't know the language. The sitemap hence becomes very difficult to navigate in multi-language situations.

NB plenselink perhaps worth to mention in the release notes: user can search on the page title, even though it is not directly visible in the sitemap (this was already possible before the fix)