iOS 7 Theme: Modify artwork and style when iOS 7 OS auto-detected at run...

Changes:
- Added iOS 7 auto detection BOOL param 'isiOS7'.
- Added additional iOS7 style artwork in the form of .png images with the "...iOS7.png" suffix.
- Added automatic switch to iOS7 artwork when iOS 7 OS detected.
- Added various margin and text color changes to work with iOS 7 style.

Note:
- When iOS 6 and previous OS detected, these code changes make no changes to default look and behavior of previous versions.

Limitations:
- Limited testing with multiple stacked buttons, background layout for '_highlighted' state is not perfect in these cases.
- No testing for side-by-side buttons.