s/utils.throttler/_.debounce/: thanks underscore

_.debounce already did the thing, we didn't need to implement this
ourselves.
Responsive Images: option to use parent width

Sometimes it makes sense for an image to fill its container instead of
using its current width as a guide. This was noticable when resizing
the browser fro very small (guide image was 'medium') to very large.
The image expanded to its natural dimensions and then *that* width
was used to choose a different size, even if *that* width was smaller
than the container.

This also adjusts the size of invisible images so they have the
correct source upon becoming visible.
guideid: parse from url

and use an actual http request instead of the fake data.