Validation errors in toolbar indicator pages don't prevent page from closing

[DonLakeFlyer]

Need to figure out how to make closing respect globals.validationError

[DonLakeFlyer]

Use mechanism that QGCDialog uses to prevent this.

[DonLakeFlyer]

The problems are more extensive than just this. Dialogs also don't validate correctly:

• Using the keyboard to close a Popup doesn't always force validation to trigger
• There can be multiple validation errors. Current code assumes only one.