Improve handbook delivering in MuseScore package

Currently, all the translated handbooks are included in the MuseScore package (exe - dmg). The handbooks together account for 36MB. Also the extra fonts for CJK languages account for 70 MB in the repository. They are finally embedded in the handbook pdf.

These are the main problems.
1/ handbook pdfs and fonts are in the repository which creates pollution
2/ the package installer grows to large
3/ it takes place on the client computer

Solutions

1. Make language dependent packages
2. Add step in Windows installer and ask what handbooks should be in/excluded
3. Make two packages: one with and one without all the pdf's
4. At first startup of MuseScore, ask user if he wants to download the handbook pdf in the system language
5. Replace the pdf for html (1/3 smaller as fonts are no more needed)