feat: Implement Dark Mode

Added styles and configurations to enable dark mode throughout the application. The dark mode features a deep blue color scheme for primary elements and improved visibility for cursor. Selected option text in mat-select now appears in white for better contrast. This enhancement provides users with the option to switch between light and dark modes seamlessly.

Changes:
- Added dark mode styles in the theme service
- Updated mifosx-theme.scss for dark mode customization
- Adjusted cursor visibility in dark mode
- Modified selected option text color in mat-select

Fixes #2021

Implemented the black-logo image into white-logo-image dynamically

src/app/core/shell/toolbar/toolbar.component.html

@@ -58,6 +58,10 @@
     <mifosx-notifications-tray fxHide.lt-md></mifosx-notifications-tray>
   </div>
 
+  <div #themeToggle>
+    <theme-toggle-component></theme-toggle-component>
+  </div>
+  
   <div #appMenu>
     <button mat-icon-button class="ml-1 img-button" [matMenuTriggerFor]="applicationMenu">
       <img src="assets/images/user_placeholder.png">