Improve progress updating, fix warnings

Caps/Download/ClassifierProgress.swift

@@ -0,0 +1,19 @@
+
+struct ClassifierProgress {
+
+    let bytesLoaded: Double
+
+    let total: Double
+
+    var percentage: Double {
+        guard total > 0 else {
+            return 0.0
+        }
+        return bytesLoaded * 100 / total
+    }
+
+    init(bytesLoaded: Double = 0, total: Double = 0) {
+        self.bytesLoaded = bytesLoaded
+        self.total = total
+    }
+}

Caps/Download/ClassifierProgressDelegate.swift

@@ -0,0 +1,5 @@
+
+protocol ClassifierProgressDelegate: AnyObject {
+
+    func classifierProgress(_ progress: ClassifierProgress)
+}

Caps/Download/ClassifierProgressObserver.swift

@@ -0,0 +1,20 @@
+import Foundation
+
+final class ClassifierProgressObserver: NSObject {
+
+    weak var delegate: ClassifierProgressDelegate?
+}
+
+
+extension ClassifierProgressObserver: URLSessionDownloadDelegate {
+
+    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
+        
+    }
+    
+    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
+        delegate?.classifierProgress(.init(
+            bytesLoaded: Double(totalBytesWritten),
+            total: Double(totalBytesExpectedToWrite)))
+    }
+}