Change hard-coded bundleID to automatically retrieved one (#202)

SecretKit/Common/BundleIDs.swift

@@ -0,0 +1,7 @@
+import Foundation
+
+
+extension Bundle {
+    public var agentBundleID: String {(self.bundleIdentifier?.replacingOccurrences(of: "Host", with: "SecretAgent"))!}
+    public var hostBundleID: String {(self.bundleIdentifier?.replacingOccurrences(of: "SecretAgent", with: "Host"))!}
+}