iOS Conf SG - logo proposal 4th iteration

4th iteration of Logo proposal for iOS Conf SG 2017 http://iosconf.sg/

Notes:
- Bring back the orange, replacing the red.
- Instead of red/green/white or orange/yellow/brown, stick with this orange/green/white combo (best of both worlds?).
- Simplified everything; colors, shadows and gradients.
- Try out different text sizes for Heading 1, 2 and sub-heading text.