Better validation messages for word/character limits

This changes the validation messages that are presented when people fill out a text input with:
- Too many characters
- Too many words

To be more consistent with the wording of other validation messages.

Relates to [card 6199](https://www.agileplannerapp.com/boards/187120/cards/6199)
Is there any good reason to move these in to the content repository with the rest of the validation messages? Or are we happy to just put them in here as it makes no difference really?