Submit Post Box needs action hook

[filosofo]

The side post box on the write page should allow additional items. One complaint about the 2.5 layout I've seen repeatedly is that people want X commonly-used feature right there on the side. The action hook in this patch will allow plugin authors to add whatever people want into the side submit box.

[ryan]

(In [6898]) Add submitpost_box action to post edit form. Props filosofo. see #5873

[ryan]

We should do the same for pages and links. submitpage_box, submitlink_box.

[filosofo]

Replying to ryan:

We should do the same for pages and links. submitpage_box, submitlink_box.

I've attached a patch that does this.

Also, since each div had the id of "submitpost" even though it was for posts, pages, or links, I changed the styling to a class named "submitbox" both in the markup and CSS and changed the ids to reflect their individual purposes.

[filosofo]

for pages and links and styling improvements

[ryan]

(In [6901]) submit box actions hooks from filosofo. fixes #5873