Creates sample project for Asset Catalogue article
Demo for using asset catalogs for icons and custom collections

With some screenshots in preparation for the writeup.
Adds code and images for sliced image example

Found an old button graphic to use. Created a screenshot as well. This
requires iOS7 to work, so updated the deployment target as well.
Completes writeup about asset catalogs

Will need reviewing at a later stage.
Adds the license header to the source files
Merge branch 'days/02-asset-catalogue'