Add Navigation events to Swift SDK

[winsmith]

Navigation signals are specific signals that have a source and target parameter and a specified signal type. Add functionality to the SDK that takes just a target and then sends a navigation signal with the correct format and the previous target as source.

Signal format is described in https://github.com/TelemetryDeck/web/issues/1491

Implementation could be in form that the SDK will keep the previous path in memory and then generates a navigation with from-to data whenever a new path is given.

• Add new documentation page about navigation evets docs#93
• Update grand-renaming/namespaces docs articles about the TelemetryDeck.Navigation namespace
• Implement a navigate(from:to:) method that sends a navigation signal in the correct format
• Implement a navigateFromPrevious(to:) method