refs #334: copy all headers to build products, as many were missing

As I cannot yet get the "correct" fix according to Apple's doc to work with Nimbus, plaeas accept this temporary fix.

This changes all headers to "public", not "project" as many were set to incorrectly before. This makes integration of Nimbus easier:
1. Add the Nimbus project to the workspace
2. Add the needed nimbus targets to the "Link Binary With Libraries" build phase of the own project.
3. Add the following path to the "Header Search Paths" of the own project: "$(TARGET_BUILD_DIR)/usr/local/include"

This makes manual copying of header files to the own project unnecessary.
If I get the complete fix right, even 3. won't be needed anymore, like written in http://developer.apple.com/library/ios/#technotes/iOSStaticLibraries/Articles/creating.html