No modules on library targets; imports Metal

Xcode 5.1.1 users are reporting problems when calabash.framework
is built with Xcode 6*.

Modules are _required_ with Xcode 6 for dylibs.

The calabash.framework and frank library do not need to use
modules, so we should turn them off.
* https://github.com/calabash/calabash-ios/issues/519
* https://github.com/card-io/card.io-iOS-SDK/issues/65
* https://github.com/CocoaPods/CocoaPods/issues/2457
Merge pull request #70 from calabash/feature/disable-modules-on-library-targets

No modules on library targets; imports Metal