Swift notification plugin (#436)

* Add Swift notification plugin

* Hash the metadata

* Validate min sendable amount

* Remove initializer as base class, UNNotificationServiceExtension, has no default initializer

* Set the PaymentMethod

* Handle PaymentDetails in SwapUpdated

* Improve payment text

lib/bindings/langs/swift/Sources/BreezSDKLiquid/ServiceLogger.swift

@@ -0,0 +1,40 @@
+import Foundation
+import os.log
+
+#if DEBUG && true
+fileprivate var logger = OSLog(
+    subsystem: Bundle.main.bundleIdentifier!,
+    category: "ServiceLogger"
+)
+#else
+fileprivate var logger = OSLog.disabled
+#endif
+
+open class ServiceLogger {
+    var logStream: Logger?
+    
+    init(logStream: Logger?) {
+        self.logStream = logStream
+    }
+    
+    public func log(tag: String, line: String, level: String) {
+        if let logger = logStream {
+            logger.log(l: LogEntry(line: line, level: level))
+        } else {
+            switch(level) {
+                case "ERROR":
+                    os_log("[%{public}@] %{public}@", log: logger, type: .error, tag, line)
+                    break
+                case "INFO", "WARN":
+                    os_log("[%{public}@] %{public}@", log: logger, type: .info, tag, line)
+                    break
+                case "TRACE":
+                    os_log("[%{public}@] %{public}@", log: logger, type: .debug, tag, line)
+                    break
+                default:
+                    os_log("[%{public}@] %{public}@", log: logger, type: .default, tag, line)
+                    return
+            }
+        }
+    }
+}