Bindings models wrapper

• Add Identity model.
• Add MessageSendReport model.
• Add Fact model.
• Add Message model.
• Add RestlikeMessage model.
• Add tests for models decoding and encoding (use example JSONs from Bindings as expected JSON schemas).

Tests/ElixxirDAppsSDKTests/FactTests.swift

+import CustomDump
+import XCTest
+@testable import ElixxirDAppsSDK
+
+final class FactTests: XCTestCase {
+  func testCoding() throws {
+    let jsonString = """
+    {
+      "Fact": "Zezima",
+      "Type": 0
+    }
+    """
+    let jsonData = jsonString.data(using: .utf8)!
+    let decoder = JSONDecoder()
+    decoder.dataDecodingStrategy = .base64
+    let fact = try decoder.decode(Fact.self, from: jsonData)
+
+    XCTAssertNoDifference(fact, Fact(
+      fact: "Zezima",
+      type: 0
+    ))
+
+    let encoder = JSONEncoder()
+    encoder.dataEncodingStrategy = .base64
+    let encodedFact = try encoder.encode(fact)
+    let decodedFact = try decoder.decode(Fact.self, from: encodedFact)
+
+    XCTAssertNoDifference(decodedFact, fact)
+  }
+}