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.

app/src/db/structs.rs

@@ -0,0 +1,39 @@
+use serde::{Deserialize, Serialize};
+use crate::config;
+
+use crate::config::structs::WakeWordEngine;
+use crate::config::structs::SpeechToTextEngine;
+
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Settings {
+    pub microphone: i32,
+    pub voice: String,
+
+    pub wake_word_engine: WakeWordEngine,
+    pub speech_to_text_engine: SpeechToTextEngine,
+
+    pub api_keys: ApiKeys
+}
+
+impl Default for Settings {
+    fn default() -> Settings {
+        Settings {
+            microphone: -1,
+            voice: String::from(""),
+
+            wake_word_engine: config::DEFAULT_WAKE_WORD_ENGINE,
+            speech_to_text_engine: config::DEFAULT_SPEECH_TO_TEXT_ENGINE,
+
+            api_keys: ApiKeys {
+                picovoice: String::from(""),
+                openai: String::from("")
+            }
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, Debug)]
+pub struct ApiKeys {
+    pub picovoice: String,
+    pub openai: String
+}