[macdoc] There may be several help sources with the same prefix, filter unique name
[macdoc] Only show in the dialog the products that are going to be updated
[macdoc] Add new search path for iOS documentation
[macdoc] Fix apple documentation feed caching to be product specific
[macdoc] Add more logging
[macdoc] Use the same item selection flawed logic than apple-doc-wizard

Both sides were doing <item /> selection incorrectly by simply getting, respectively, the first and the last item. To be accurate, we need to sort them according to the <updated /> field.

To stay compatible with the released version of XamMac and Xam.iOS, simply reuse their style.