Proposed Change: remove STDIO operation from GDAXDownloaderProgram

[PaoloOranges]

It would be beneficial to move all the dependency from STDIO (ie Console.ReadLine() and Console.WriteLine()) from GDAXDownloaderProgram to Program.cs.
It would remove dependency from GDAXDownloaderProgram allow it to be called in other functions and not depends on user input to return

Expected Behavior

GDAXDownloaderProgram.GDAXDownloader(tickers, resolution, fromDate, toDate); would return without having to wait for IO from Console

Actual Behavior

GDAXDownloaderProgram.GDAXDownloader(tickers, resolution, fromDate, toDate); does not return after finishing downloading data since it wait for Console.ReadLine

Potential Solution

Move IO Console operation to Program.cs.
Since the change is no more than 5 min: #13
I will close the PR if refactor is not accepted

Reproducing the Problem

System Information

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