Implement #1108 "fr:grid: ability to freeze n first rows"
Improve active alert algorithm

Don't show default alerts if there are more specific alerts that apply.
Fix JS error following d479381b76f472e3faf0afe660ece37c433126e8
IntelliJ project files
Only hide top-level LHH in repeated grids
Revise validation dialog

- now lists validations, not alerts
  - required validation
  - datatype validation
  - constraint validations
- clearer notion of default/global error alert message