use blog post header image thumbnails for kinoupdates widget

[0x70b1a5]

Problem

Blog post images in the KinoUpdates widget load fullsize images rather slowly.

Solution

• [x] Update the blog API to create and serve thumbnail sized images.
• [x] Query the thumbnails in the widget.

Testing

• [x] Verify loading of images is snappy.
• [x] Inspect image source: verify image ends with -thumbnail.