Add button to interface for flipping sequence (mock-up)

This is non-functional. It's just to show a potential UI implementation for flipping the sequence to its reverse compliment. This is to address issue gear-genomics#14.

client/src/index.html

@@ -143,6 +143,11 @@ <h1 class="display-4 app-name">Pearl</h1>
             </div>
           </div>
           <br />
+          <div id="result-actions" class="row">
+            <button type="submit" class="btn btn-outline-secondary" id="btn-flip">
+              Flip sequence
+            </button>
+          </div>
           <div id="result-info" class="alert alert-info d-none" role="alert">
             <i class="fas fa-spinner spinner"></i>
             Analysis is running, please be patient.