Adding support for iPhone 6 Plus icons

JIRA ticket: https://jira.appcelerator.org/browse/TIMOB-17663

- For App icon, 180x180: Added new `-60@3x.png`
- For Spotlight search results icon, 120x120: Verified it uses existing `-60@2x.png`
- For Settings icon, 87x87: Added new `-Small@3x.png`

Tested this in Simulator by overlaying unique text on each icon.

Reference: https://developer.apple.com/library/prerelease/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html#//apple_ref/doc/uid/TP40006556-CH27-SW1