cp#1000072: Improve on-load updates of external links.

* Load all linked external sources up front, rather than on-demand after
  the cache purge.

* Try to pre-populate updated caches rather than leaving them blank and
  wait until it gets filled during formula calculation.

* Disable polling of stale doc shell instances while the update is
  on-going.  This improves the update performance especially when the update
  takes a long time.

* Only close one doc shell instance at a time, even when there are multiple
  stale doc shell instances that need to be closed, to prevent too long of
  a pause.

* Show progress bar during the update to give the user some visual feedback
  of the progress.

* Skip loading of styles for the linked external document shells.  We don't
  need them.  For now, this is ODS only.

* Minor performance improvement of ODS import.

Conflicts:
	include/sfx2/sfxmodelfactory.hxx
	sc/inc/sc.hrc
	sc/inc/xmlwrap.hxx
	sc/source/core/data/documen8.cxx
	sc/source/filter/xml/xmlimprt.cxx
	sc/source/filter/xml/xmlwrap.cxx
	sc/source/ui/docshell/docsh.cxx
	sfx2/source/doc/objxtor.cxx

Change-Id: I80aa71fa27e4960e9256253369aa898dd542c9b5