[META][UX] Better "Recent content" block

I started tweaking #4020 and quickly got into multiple interesting rabbit holes ...in the end I got a very nice result, but there were multiple changes in all sorts of places, and I'm afraid that a single PR would make this unreviewable. So I'm filing this as a meta issue, to get all the bits implemented incrementally.

Here's what I have so far (admin user - CSS still needs some work):

Changes:

• [ ] Zebra stripping the rows in the block, for better scannability.
• [ ] Tweaked theme_more_link() to allow custom "more" link text/properties, and made that "All recent content" for this block.
• [ ] Made the "Number of recent content items to display" field in the block settings a number field instead of a select with limited options.
• [ ] Make the edit/delete links dropbuttons instead.
• [ ] Adjust the colspan of the content/author column cells, depending on whether the operations buttons are shown or not for each row (based on permissions the current user has).
• [ ] Add checkbox in the block settings, to show the operations dropbuttons column or not.
• [ ] Proper "submitted by" info, pulled from the content type settings, instead of just the author username
• [ ] Add checkbox in the block settings, to show the "submitted by" info or not.
• [ ] Render the username link via a new [node:author:link] token (see https://www.drupal.org/project/token/issues/1176592 and https://www.drupal.org/project/token/issues/698242)
• [ ] Moved sevenDropButtonWidths() that helps calculate dropbutton widths from core/themes/seven/js/script.js to core/misc/dropbutton.js (and renamed it to dropButtonWidths()), so it can be used in Basis and other themes.

Happy to discuss each of these changes and either do or not.

Here's a few more screenshots...

• anonymous user viewing the page ("submitted by" info hidden):

  

• another_user logged in ("Editor" role, author of the second piece of content in the table - has no permission to delete own content):

  

• block settings dialog: