Move all icons into skin/icons directory
As part of trac#6322 we want to clean up the repository's directory structure. While it has improved naturally in the last few months, the icons we use are still spread all over the skin directory. Therefore we should consolidate them in the skin/icons directory.
What to change
- Move contents of skin/mobile/ to skin/icons/mobile/
- Move contents of skin/social/ to skin/icons/
- Move contents of skin/updates/ to skin/icons/updates/
- Move skin/abb-logo.png, skin/abp-64.png, skin/abp-128.png and skin/abp-logo.svg to skin/icons/
- Update references to any of the moved files