Merge pull request #452 from anthonyfok/l10n-zh

Initial l10n for Chinese (zh_CN, zh_HK, zh_TW)
add credits for (skeleton) Chinese translation
bindir() might return false...
update chlog
simplify session management handling
TODO test behaviour under KDE, also store documents and open document per window (sharing code with named sessions support)
save list of open document and current named session name when save QT session
better restore list of open documents
Unified diff tab added, see issue #436
Added save button #436
change font to monospace
Further development of file saving, including better filenames.
adding ly code highlighter in diff tab
diff highlighting
[rewrite xml export] basic handling of notes and rests
Merge pull request #453 from PeterBjuhr/convert-ly-diff

Convert ly diff
[rewrite xml export] bar attributes
[rewrite xml export] accidentals
[rewrite xml export] file structure
[rewrite xml export] inner structure
[rewrite xml export] scaler/tuplets