🎨 Add theme support

- Move root (var) style properties to `/assets/css/themes.scss`
- Improve mobile navigation
- Create section component for the collapsable sections.
- Create logo component, so color can be changed.

- Add settings page
- Add option to select theme color
- Add option to select theme background
- Add option to enable/disable multi-colored frames.

- Add settings to VueX Store
- Persist VueX store in LocalStorage.

assets/css/themes.scss

@@ -0,0 +1,39 @@
+/**
+  Main Themes:
+
+  - dark (default)
+  - light
+ */
+
+// Dark is the default theme variant.
+:root {
+  --bg-dark-color: #000000;
+  // Background color
+  --bg-color: #121212;
+  // Text color
+  --fg-color: #FFF;
+
+  // Error color
+  --err-color: #393939;
+
+  // Active color
+  --ac-color: #51FF0D;
+  // Active text color
+  --act-color: #121212;
+}
+
+:root.light {
+  --bg-dark-color: #ffffff;
+  // Background color
+  --bg-color: #F6F8FA;
+  // Text color
+  --fg-color: #121212;
+
+  // Error color
+  --err-color: invert(#393939, 1);
+
+  // Active color
+  --ac-color: #51FF0D;
+  // Active text color
+  --act-color: #121212;
+}