Update APIX-CT-ConverterPlugin.cc

Replaced APIX-CT_ConverterPlugin by the working version by Stefano Terzo(cherry picked from commit 8260408a206ee6d1905be4f1cfe02074759456d7)
APIX-MC-ConverterPlugin removed
as of no use since 2010
(cherry picked from commit 3cd1fe69a591d726a98685512b0c1c473d878cf5)
updated release notes with info for v1.2.1
(cherry picked from commit 5606d2fc35c0af29c62e1b8126e5b3a6fc849887)

Conflicts:
	README.release_notes