Add notice if agent isn't running (#47)

* Add agent checker
* Check on foreground

Secretive/Controllers/AgentStatusChecker.swift

@@ -0,0 +1,33 @@
+import Foundation
+import Combine
+import AppKit
+
+protocol AgentStatusCheckerProtocol: ObservableObject {
+    var running: Bool { get }
+}
+
+class AgentStatusChecker: ObservableObject, AgentStatusCheckerProtocol {
+
+    @Published var running: Bool = false
+
+    init() {
+        check()
+    }
+
+    func check() {
+        running = secretAgentProcess != nil
+    }
+
+    var secretAgentProcess: NSRunningApplication? {
+        NSRunningApplication.runningApplications(withBundleIdentifier: Constants.secretAgentAppID).first
+    }
+
+}
+
+extension AgentStatusChecker {
+
+    enum Constants {
+        static let secretAgentAppID = "com.maxgoedjen.Secretive.SecretAgent"
+    }
+
+}