Display character limit for students

[Jeremy Hopkins]

It would be useful to show students the character limit before they enter text / try to save, or better still show “characters remaining” as they typed below each field. The screen recording below explains this in more detail:

https://tinyurl.com/spoukrs

[Frédéric Massart]

Display character limit for justification fields. Fixes #44

→ <<cset d15740156a1f>>