Change many classes in oox to be based on ContextHandler2 instead of
ContextHandler. That supposedly adds MCE support.

This is a minimal initial effort. It compiles and links but doesn't work
(CppunitTest_chart2_export fails). Follow-up coming...

Change-Id: If89117abd48cfead468633fd7fce1ea785f6f420
Reviewed-on: https://gerrit.libreoffice.org/4577Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>