Link to admin page of missing parent post when pre-flight fails.
Save batch title in cookie

Resolve #47
Store batch data in database after pre-flight
Improve possibility to modify post before it gets added to batch
Remove expensive pre-flight check.

When a batch was sent to production a HTTP request per included image was made to stage to ensure that the image really existed and that it was accessible. This check was really expensive.
Pre-flight check images on content stage
Remove inefficent pre-flight check
Important performance improvement
Print parent page in Edit Batch post list