Major classes, variables and strings refactoring. Code cleanup.

app/src/main/res/drawable/ic_exit_app.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="32dp"
+    android:height="32dp"
+    android:viewportWidth="24.0"
+    android:viewportHeight="24.0">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M10.09,15.59L11.5,17l5,-5 -5,-5 -1.41,1.41L12.67,11H3v2h9.67l-2.58,2.59zM19,3H5c-1.11,0 -2,0.9 -2,2v4h2V5h14v14H5v-4H3v4c0,1.1 0.89,2 2,2h14c1.1,0 2,-0.9 2,-2V5c0,-1.1 -0.9,-2 -2,-2z" />
+</vector>