Make AdjustIo a static class

Refactor and clean up
Make log levels more subtle
Add special setters for NSMutableDictionary
Restructure session and event handling

Prepares tracking of offline sessions and events
Remove user agent log
Add request timeout
Add tracking queue for asynchronous requests

Add locks
Refactor
Add and improve logs
Add parameter checks
Add string constants for keys and fields
Rename userDefaults keys
Improve checkAppToken, add TODOs
Add AESessionContext
Add static methods to AELogger
Add AESessionContext
Use AESessionContext in AdjustIo
Create defaultLogger
Add AETimer, move session logic to sessionContext
Add classes ActivityPackage, PackageBuilder, SessionState
Extend sessionHandler
Rename SessionContext to SessionHandler