another speedup attempt for index.html:

 carousel images to use thumbnails instead, 1 blocking js removed for page (sidebar.js)

as discussed in and further addressing #2477

Some notes: We were generating thumbnails already for the examples gallery, however only for the first image of each set. Thus, some of the ones we desired for the carousel did not have their own thumbnails.
Second problem was that because of the example gallery thumbnail dimensions, quite a few of the thumbnails didn't work well in the carousel directly, due to extra white-space. Thus, during the thumbnail generation, I added that the few needed ones or ones needing carousel-dimensions, be generated too and written to the _images directory.

Last thing is that I removed the sidebar script for the front page which acts as a 'blocking script' according to google pagespeed. Hopefully these changes will add to the speedup of the index a bit further