Resolve Xcode 9 compatibility issues

[ecaselles]

This PR is a rebased version of #702 to pick the changes introduced in #703.

• [x] update project to recommended settings
• [x] update dependencies
• [x] resolve all project warnings.
• [x] fix odd test crashing in iOS 10
• [x] update Travis configuration to use Xcode 9.2

It is part of #699.

Thanks @SergeyKuryanov for all the hard work 👏