Support for thumb and frame images with captions.

* VisualEditor.hooks.php
** export URL to magnify clip as a configuration variable so thumbnail image can render correctly

* ve.ce.Surface.css
** add CSS styling to make image captions look the same way in edit mode as they look in the view mode

* ve.ce.ParagraphNode.js
** add CSS class ve-ce-generated-wrapper if it is a generated wrapper

* ve.ce.MWImageCaptionNode.js
** make image caption rendering match the view mode

Change-Id: I0cd1b25e8f8355e0500aabc90e7c4cdf591545f3
Merge "Support for thumb and frame images with captions."