Command `install` will produce universal iOS lib

Add module `install_universal_ios_static_library` to install universal
iOS (iphoneos + iphonesimulator) static library. Run function from this module
after real `FILE(INSTALL ...` command in `cmake_install.cmake` to
overwrite library. Two variables added to install script:
* INSTALL_UNIVERSAL_IOS_STATIC_LIBRARY_NAME (target name)
* INSTALL_UNIVERSAL_IOS_STATIC_LIBRARY_TOP (top dir, i.e. PROJECT_BINARY_DIR)