Add 'Copy Username' button (#691)

This adds a 'Copy Username' button above the 'Copy Password' button in
the dropdown for individual entries in the safe. This matches the
capabilities of the desktop app, where you can right-click on any entry
and get options for both 'copy password' and 'copy username'.

src/app/vault/ciphers.component.html

@@ -37,6 +37,11 @@
                         </button>
                         <div class="dropdown-menu dropdown-menu-right" aria-labelledby="dropdownMenuButton">
                             <ng-container *ngIf="c.type === cipherType.Login && !c.isDeleted">
+                                <a class="dropdown-item" href="#" appStopClick
+                                    (click)="copy(c, c.login.username, 'username', 'username')">
+                                    <i class="fa fa-fw fa-clone" aria-hidden="true"></i>
+                                    {{'copyUsername' | i18n}}
+                                </a>
                                 <a class="dropdown-item" href="#" appStopClick
                                     (click)="copy(c, c.login.password, 'password', 'password')" *ngIf="c.viewPassword">
                                     <i class="fa fa-fw fa-clone" aria-hidden="true"></i>