Web: Updated introduction.itexi - Easier Editing

Web: Updated introduction.itexi - Easier Editing

Easier Editing Section

'... no longer being
actively devloped' section.

Moved MuseScore here from the
'Other programs ...' section.

http://lists.gnu.org/archive/html/
lilypond-user/2014-02/msg00087.html

Added OOoLilyPond. It appears still
to work with OpenOffice 4 but not
with the up and coming v 5.

http://lists.gnu.org/archive/html/
lilypond-devel/2015-07/msg00006.html

Rearranged existing entries to put
them in alphabetical order.