Update to iOS device imagery, positioning, icons, and readme

- Updated iPhone imagery:
  - iPhone 4/4S imagery left alone and still works with 3.5 inch sim
  - iPhone 5 imagery left but removed from code references
  - iPhone 5s imagery added, included a landscape state and elseif statements for the simulator with appropriate positioning
  - Replaced iPad imagery with iPad Air imagery, updated associated positioning
- Updated the Readme file to go into greater depth, as well as going into detail on manually adding applications to the simulator if SimFinger doesn't work
- Updated the Appstore icon