Job listing form should take employer details before job description

[jace]

The job listing form currently asks for the job description before the employer's details. However, many validation failures happen in the relatively static employer details section.

The form should be reversed. The first question should be the email address, which autofills employer details, and once those are collected, an empty draft post is created and the user is redirected to edit it. The current listing form can be used for this, in case the user wants to change employer details. (This does make the employer logo edit tricky, however.)

The edit form should now autosave, as all mandatory fields are already collected before the draft post is created. Further, expensive validations such as the dupe check should be performed in the submit phase (Draft to Pending state transition). Link validity check may remain in the edit form because it is relevant during edit, and because lookups are cached.