refractor: login module (#283)

* Refractor components.
* Shift language and footer component to shared module.
* Replace mat-icons by font-awesome icons.
* Add comments.

Fixes #284

src/app/shared/file-upload/file-upload.component.ts

@@ -21,7 +21,7 @@ export class FileUploadComponent implements OnInit {
 
   /**
    * Uploads a file.
-   * @param {any} $event The file input change event.
+   * @param {any} event The file input change event.
    */
   onFileSelected($event: any) {
     this.fileName = $event.target.files[0].name;