Limit slugs to 150 characters

Use the babosa gem to remove punctuation and apply the safe truncate
when we override `normalize_friendly_id`

https://www.pivotaltracker.com/story/show/47813037
Warning on the title when it is longer than 65 and 150

Also display the slug on the edit form in a disabled text field
Merge pull request #438 from alphagov/slug-length-changes

Limit slugs to 150 characters

https://www.pivotaltracker.com/story/show/47813037
https://www.pivotaltracker.com/story/show/32487033