bnc#885548: Initial work on importing revisions from xlsx.

Change-Id: Ie0528490d024093cbabf38541fe70be96a9caa2e
(cherry picked from commit b92fdaa1a40bd54d279b4ac2faf19bf15468cc2f)
bnc#885548: Adjust xlsx export of revisions to get it to work in Excel.

(cherry picked from commit fa44673e154ed4fb0b518b8850e2f6e4b9069531)

Conflicts:
	sc/source/filter/inc/XclExpChangeTrack.hxx
	sc/source/filter/xcl97/XclExpChangeTrack.cxx
	sc/inc/cellvalue.hxx
	sc/source/core/data/cellvalue.cxx

Change-Id: I0058d9ddfea545390e615a3030171a366e333c85