Check Greek symbol map

[zuevval]

When I added Greek characters from Golubina's book to AngelinaReader, a user pointed out that it is Soviet mathematical Greek Braille, not modern literary Greek Braille. Therefore, either the symbol map should be changed in our app, or this fact should be mentioned in the lessons and in the browser help.

[zuevval]

If we change the mapping to literary Greek, it's probably wise to add digraphs (see here)

[zuevval]

I asked VN and she said that, indeed, the Braille mapping may vary across different areas (e.g. there are at least 3 standards for contractions in UEB). But in our introductory course, we should leave Greek as in Golubina (and mention the existence of alternative mappings).

[winter-yuki]

This choice should be mentioned in the help of the course and practice, I guess.

[zuevval]

This choice should be mentioned in the help of the course and practice, I guess.

Uhm, I'd rather add it to the browser help, but not to the course/practice help - they are already quite long