Enhance annotation maximum length handling

[niknetniko]

This pull request:

• Increases max annotation length to 10.000 (this should still be well within the database column limit)
• Adds client side limitations and validations: this should prevent you from typing too many characters, and if you do manage to type too many characters, the browser validations should be shown. Submitting empty annotations is also impossible now.
• Shows a counter in the bottom right how many characters are used:

• Tests were added

Closes #3164 .

[pdawyndt]

Dodona style for large numbers: thin space instead of dots to separate the thousands.