More renaming; text -> plain.

More renaming; text -> plain.

sed -i "s/TextTextContent/PlainText/g" src/lib/*.cc src/lib/*.h src/wx/*.cc src/wx/*.h src/tools/*.cc test/*.cc
sed -i "s/text_text/plain_text/g" src/lib/*.cc src/lib/*.h src/wx/*.cc src/wx/*.h src/tools/*.cc test/*.cc src/lib/wscript
mv src/lib/text_text_content.cc src/lib/plain_text_content.cc
mv src/lib/text_text_content.h src/lib/plain_text_content.h
mv src/lib/text_text_decoder.cc src/lib/plain_text_decoder.cc
mv src/lib/text_text_decoder.h src/lib/plain_text_decoder.h