Add a debug Option to the Tracker.

[brototyp]

Right now it is pretty hard to debug the tracker if something goes wrong or not as expected. I think we should be more verbose at some points without being to talky.

• What are events that we want to log per default?
  • Failed dispatching?
• How should we categorize logs? Just debug yes/no? Or more complex verbose/debug/info/warning/error? I think debug yes/no should be enough.
• How should we log the messages? Always to the console?

[brototyp]

How about defining a simple logger protocol like so:

protocol Logger {
    func log(message: String)
    func debug(message: String)
}

final class ConsoleLogger: Logger {
    func log(message: String) {
        print("[PiwikTracker] | \(message)")
    }
    func debug(message: String) {
        print("[PiwikTracker] Debug | \(message)")
    }
}

let logger: Logger = ConsoleLogger()
logger.log(message: "This is an important message!")
logger.debug(message: "This is just a debug message.")

For now we just use the ConsoleLogger. In the future we can then give users the option to create a custom logger that passes the messages to their own logging mechanism.