Bundle select2 as npm dependency instead of local files

- Added select2 as npm dependency
- Removed local select2 library files to eliminate duplication
- Updated webpack config to copy select2.css to dist folder
- Added global jQuery attachment fix for select2
- Updated README to reflect bundled dependency approach
- Enabled select2 demo functionality

demo/index.html

@@ -65,7 +65,7 @@
 
             <div class="container">
                 <h3>Test X-Editable Select2</h3>
-                <p>Click to select from a larger list with search (Note: Requires select2 library):</p>
+                <p>Click to select from a larger list with search functionality:</p>
 
                 <a
                     href="#"
@@ -75,7 +75,7 @@
                     data-pk="104"
                     data-title="Select Country"
                 >
-                    Click to select country
+                    United States
                 </a>
             </div>