Public headers in a directory named `framework` should be linked in the sandbox

[Downloader] Run prepare_command even when skipping the cache

[Resolver] Take supported platforms into account when resolving

[TargetIntegrator] Ensure to reset the contents of the Manifest.lock Script Phase

Always codesign if target is codesigned, not just if required.

Fixes an issue which prevented using a custom `CONFIGURATION_BUILD_DIR` when integrating CocoaPods via dynamic frameworks.

Support for the new `watchos` platform

Skipped by `examples:build` for now, because it breaks with Xcode < 7.0