Optimized images

All images optimalized via PNGGauntlet. The image quality unchanged, but
the files became smaller.
Update jQuery files

Demo theme: v1.10.2 -> v1.11.1
Backend: v2.0.3 -> v2.1.1
Furthermore I renamed the jquery-2.0.3.min.js file because of easy to
update jQuery in future.
Merge pull request #800 from gergo85/master

Optimized images and update jQuery