Improve appearance of "choose from library" link for headers and backgrounds

[sabreuse]

As seen <a href="​http://wordpress.com/wp-admin/images/screenshots/flex-header-media-library.png">here</a>, the link we added to choose headers and backgrounds from the media library looks bad. This puts "or choose from image library" inline so it all flows better.

There's an odd space in the <a> tag in the first part of the patch: < a id="...">.

Thanks for catching that - fixed in in 20737.2

Perhaps we should also escape $image_library_url (done in 20737.3.diff​).

In media_buttons(), get_upload_iframe_src() is escaped:
http://core.trac.wordpress.org/browser/tags/3.3.2/wp-admin/includes/media.php#L376

I can't see what the new patch makes it look like (not on a computer with svn etc right now), but one concern I'd have is that if it's inline the width would be an issue on smaller screens/devices. It's pretty late in the game to change layout stuff with no testing since we're hopefully doing rc1 today.

Here's what it looks like with the patch: 20737.after.png​.

"or" on its own line is how we have it in the uploader. Inline is how we do it for internal links. Thinking leave for now, standardize all the "or"s in 3.5 instead.

It is on its own line in the uploader only because it is a larger font and a better visual. Here, it is simply super ugly. This was reported by sabreuse at the request of ryan and me.

More importantly, though, this string is improperly internationalized. (The uploader isn't much better.) We should make a change here regardless.

Two sections. PoC for custom header.

20737.4.2.diff​ is an attempt to use a consistent formatting in both custom-background.php and custom-header.php while keeping the same appearance as on a-tale-of-two-sources.png​.

In [20884]:

Improve appearance of "choose from library" link for headers and backgrounds. Props SergeyBiryukov, sabreuse. see #20737

In [20885]:

Move from 'Upload Image' to 'Select Image' as this section now includes choosing an image from the media library. see #20737.