Truncate messages in warning triangle tooltip and dashboard events table

[MetRonnie]

These can be quite long and can even include traceback sometimes.

Also save items per page for the dashboard events table, in local storage.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Docs not needed.

[MetRonnie]

line-clamp is still not really supported, so have to include these webkit-prefixed styles as well - which are widely supported - https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/line-clamp