Add all graphics from Yuri web design

[mblomdahl]

This task/issue is about adding all graphics assets from Yuri that is needed to create the intended theme design, i.e.

1. favicon images
2. logo variants for different devices and screen resolutions (with documenting/instructive naming, e.g. consulting-logo-tablet.png)
3. background images for different devices and screen resolutions (with instructive naming, e.g. it-services-bg-640px-iphone.png, consulting-bg-768px-tablet.png)

Add these assets in a single commit referencing this ticket and open a PR to merge it to master.