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/ResourceHelper.swift

@@ -0,0 +1,19 @@
+import Foundation
+
+public class ResourceHelper {
+    public static let shared = ResourceHelper()
+    
+    private init() {/* must use shared instance */}
+    
+    public func getString(key: String, fallback: String) -> String {
+        return getString(key: key, validateContains: nil, fallback: fallback)
+    }
+    
+    public func getString(key: String, validateContains: String?, fallback: String) -> String {
+        if let str = Bundle.main.object(forInfoDictionaryKey: key) as? String {
+            if validateContains == nil || str.contains(validateContains!) {
+                return str
+            }
+        }
+        return fallback
+    }}