Fixed Cocoapods support

Updated to Xcode 9 / swift 4

Fixed dependencies versions to support Xcode 8

1. Implemented multiple sessions support for same participant
2. Introduced InsensitiveDataStorage protocol
3. Fixed expired sessions/otc/ltc removal
4. Added logging in Debug configuration
5. Added documentation
6. Lots of small fixes, internal changes and refactoring

Fixed

• Do not remove OTC keys when rotate keys