Publicize to different accounts depending on the category of the post

It would be cool to have the ability to publicize to different Facebook accounts based on the category of the post. Instead of choosing it manually, we can automate this and allow users to choose different Facebook pages for different post categories only once. They would be able to change it at any time, though.

This idea came up in 897010-hc.

No implementation file or test is named. Start by reviewing the existing Publicize flow for manually selecting Facebook accounts and the discussion referenced in 897010-hc; done means users can assign different Facebook pages to post categories and change those assignments later.

Written by the indexing model from the issue text.