Edit Image modal:
- Fix issue with adding a link to an image that didn't have one previously.
- Adjust the look-and-feel of the advance options toggle so that it becomes a section heading that can be open/closed.
- Add a Custom Size option to the size drop-down that reveals fields for soft-resizing the image inserted into the post.
Props gcorne, and props sdasse for the design help, see #27366

git-svn-id: https://develop.svn.wordpress.org/trunk@27918 602fd350-edb4-49c9-b593-d223f7449a82