First version extracted and modified from Alicerce 🙏

This was mostly extracted from Alicerce with minor changes (probably for worse)
This isn't tested yet ⚠️ 🚧

Changes:

• Used Atomic copied from ReactiveSwift
• Not used type erased AnyAnalyticsTracker
• Slight changes to MultiTracker and AnalyticsTracker (removed associatedType's and modified track method with generic types)
• Update Atomic with new Swift 5 accessor _modify