App architecture modifications.

Now GUI and the app itself is divided into two different binaries.
The app also provides system tray icon.
Whereas the GUI can be used to configure the app.

gui/src-tauri/src/main.rs

@@ -0,0 +1,48 @@
+// Prevents additional console window on Windows in release, DO NOT REMOVE!!
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+use std::path::PathBuf;
+
+use once_cell::sync::OnceCell;
+use platform_dirs::{AppDirs};
+
+// expose the config
+mod config;
+
+// include log
+#[macro_use]
+extern crate simple_log;
+mod log;
+
+// include db
+mod db;
+
+// include tray
+mod tray;
+
+// include tauri commands
+// mod tauri_commands;
+
+// some global data
+static APP_DIRS: OnceCell<AppDirs> = OnceCell::new();
+static APP_CONFIG_DIR: OnceCell<PathBuf> = OnceCell::new();
+static APP_LOG_DIR: OnceCell<PathBuf> = OnceCell::new();
+static DB: OnceCell<db::structs::Settings> = OnceCell::new();
+
+fn main() -> Result<(), String> {
+    // initialize directories
+    config::init_dirs()?;
+
+    // initialize logging
+    log::init_logging()?;
+
+    // log some base info
+    info!("Starting Jarvis v{} ...", config::APP_VERSION.unwrap());
+    info!("Config directory is: {}", APP_CONFIG_DIR.get().unwrap().display());
+    info!("Log directory is: {}", APP_LOG_DIR.get().unwrap().display());
+
+    // initialize database (settings)
+    DB.set(db::init_settings());
+
+    Ok(())
+}