Fix wikidata singlenode manifest

- replace Mw-extension with Mediawiki_singlenode::Mw-extension
- Remove the redundant exec['update-script'] defined in the wikidata
  clases
- Tinker with ordering a lot so that update.php gets called after all
  the extensions are installed
- Fix up (or, possibly, break) order of operations for
  rebuildLocalisationCache.php

Change-Id: I59c02996cae7b1bd5402aad1576da2e21cffc9be
Merge "Fix wikidata singlenode manifest" into production