Fixes bug #670 apply label customisation easy/good/hard uniformly across buttons & menu

[ronzulu]

This fixes bug:
#670

Minor issues for some non-English languages

For some languages, the translation for the difficulty levels is slightly different depending on context, e.g. for Easy in Russian:

REVIEW_EASY_FILE_MENU: "Повторение: Легко",
REVIEW_NOTE_EASY_CMD: "Повторять заметку как Лёгкую",

i.e. Легко verses Лёгкую

I'm assuming that any grammatical error introduced by using a single term for Easy etc is minor, and would still be understood by users. Also, I assume that the translation of "Review note as" could be modified in affected languages to make this update grammatically correct.

REVIEW_DIFFICULTY_FILE_MENU: "Review: ${difficulty}",
REVIEW_NOTE_DIFFICULTY_CMD: "Review note as ${difficulty}",

Screenshots

Previously implemented:

Now also:

[st3v3nmw]

Thanks for the fix!