feat: Reimplement the Zooming Image Tool

This recreates the Zooming Image Tool template for the HTML block.  It
does it in such a way that doesn't depend on any external resources:
both the loupe code and sample image are inlined.

Some benefits to this version are:

* We can now maintain the loupe javascript code properly

* Because the javascript is included in the contents of the block
  itself, the course author can customize it as needed

* As opposed to the previous iteration, the magnified image URL is now
  optional: if it's not present, the regular image will be used for
  magnification

This also removes some CSS left over from the previous iteration.

cms/static/sass/elements/_vendor.scss

@@ -66,13 +66,6 @@
   z-index: 100000 !important;
 }
 
-//jQuery loupeAndLightbox Plugin
-.zooming-image-place {
-  .larger {
-    left: 0 !important;
-    bottom: 100% !important;
-  }
-}
 // ====================
 
 // reset styles to remove ui-lightness jquery ui theme from the tabs component (used in the add component problem tab menu)