MBS-7867: Fix relationship edits with unchanged attributes

The WS::js::Edit controller turned a missing "attributes" parameter in
a relationship edit (indicating no changes to the attributes) into an
empty array of attributes, leading to the removal of any attributes
the relationship may have had, contrary to the user's intention.
Add test for MBS-7867
Add test case for removing a relationship attribute via WS::js
Don't ever bundle the last/current batch into a previous sitemap.
Merge branch 'sitemap-final-exclusion-rebase'

* sitemap-final-exclusion-rebase:
  Don't ever bundle the last/current batch into a previous sitemap.
Add sitemap support for the aliases tab.
Add support (optional, off by default) for pinging search engines when sitemaps are built.
Merge branch 'sitemaps-aliases-pinging-rebase'

* sitemaps-aliases-pinging-rebase:
  Add support (optional, off by default) for pinging search engines when sitemaps are built.
  Add sitemap support for the aliases tab.
Merge remote-tracking branch 'chirlu/mbs-7867'

* chirlu/mbs-7867:
  Add test case for removing a relationship attribute via WS::js
  Add test for MBS-7867
  MBS-7867: Fix relationship edits with unchanged attributes