VEX-5682: iOS Swift Conversion (#11)

Converts ios implementation from objective-c to swift.

ios/Video/DataStructures/VideoSource.swift

@@ -0,0 +1,31 @@
+
+struct VideoSource {
+    let type: String?
+    let uri: String?
+    let isNetwork: Bool
+    let isAsset: Bool
+    let shouldCache: Bool
+    let requestHeaders: Dictionary<String,Any>?
+    
+    let json: NSDictionary?
+    
+    init(_ json: NSDictionary!) {
+        guard json != nil else {
+            self.json = nil
+            self.type = nil
+            self.uri = nil
+            self.isNetwork = false
+            self.isAsset = false
+            self.shouldCache = false
+            self.requestHeaders = nil
+            return
+        }
+        self.json = json
+        self.type = json["type"] as? String
+        self.uri = json["uri"] as? String
+        self.isNetwork = json["isNetwork"] as? Bool ?? false
+        self.isAsset = json["isAsset"] as? Bool ?? false
+        self.shouldCache = json["shouldCache"] as? Bool ?? false
+        self.requestHeaders = json["requestHeaders"] as? Dictionary<String,Any>
+    }
+}