Add headers and precompiled libraries for libcurl support on all platforms
 - libcurl has platform-specific header files because it performs architecture-related checks at compile time
 - cross-compilation of libcurl is prohibitively difficult, keeping precompiled static libraries is much easier
Delete unused curl files
Merge branch 'libcurl-support'

Conflicts:
	Makefile
	android/jni/Android.mk
	android/jni/Application.mk
	ios/TangramiOS/TangramiOS.xcodeproj/project.pbxproj