Add Shared Core for iOS platform
- Add shared Core logic in ios platform helpers and constructors in factory
 - Add high level functions to get the message or the new chat room from a push notification
 - Allow wrappers to use linphone logger
 - Add core option to send imdn without being registered
 - Improve linphone_core_stop()
 - Move the paths functions to the same place for all platforms and add paths for iOS shared file system
 - Add shared core tests and modify LinphoneCoreManager to create shared cores