Simple Refactoring MainActivity

[wwxiaoqi]

Significant changes:

1. Moved some existing constants to AppConfig.
   Improve AppConfig configuration constants. b22f7d7
   Extract config constants to AppConfig.

2. Extracted parts previously managed by MainActivity into several separate components:

• AppAssetManager: Manages application assets, currently used for unpacking and managing the app.zip version.
• HttpServerManager: HTTP server manager, handles starting and stopping the HTTP service.
• KernelManager: Kernel lifecycle manager, handles starting and stopping the kernel.
• SyncManager: Data synchronization manager, performs data synchronization asynchronously. Note: Replaced the original Boolean with AtomicBoolean to improve thread safety.
• WebViewManager: Primarily handles WebView lifecycle and configuration. Note: Uses WeakReference to prevent memory leaks.

Extract asset management to AppAssetManager.
Extract HTTP server to HttpServerManager.
Extract kernel management to KernelManager.
Extract sync logic to SyncManager.
Extract WebView management to WebViewManager.

3. Reorganized the original project structure.
   new folder has been organized by modules.

  org.b3log.siyuan/
  ├── activity/                                   # Activity related
  │   ├── MainActivity.java
  │   ├── BootActivity.java
  │   ├── ShortcutActivity.java
  │   └── RedirectUriReceiverActivity.java
  ├── manager/                                   # Manager classes
  │   ├── AppAssetManager.java
  │   ├── HttpServerManager.java
  │   ├── KernelManager.java
  │   ├── SyncManager.java
  │   └── WebViewManager.java
  ├── service/                                   # Service classes
  │   ├── KeepLiveService.java
  │   └── NotificationReceiver.java
  ├── bridge/                                    # JavaScript bridge
  │   └── JSAndroid.java
  ├── util/                                      # Utility classes
  │   ├── Utils.java
  │   └── AndroidBug5497Workaround.java
  ├── config/                                    # Configuration classes
  │   └── AppConfig.java
  └── App.java                                   # Application class