Add showing and modifying user name (#306)

Make sure to use the user name field everywhere

Add showing and modifying user name

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/306
Co-Authored-By: konrad <konrad@kola-entertainments.de>
Co-Committed-By: konrad <konrad@kola-entertainments.de>

src/components/misc/user.vue

@@ -6,8 +6,8 @@
 			:width="avatarSize"
 			alt=""
 			class="avatar"
-			v-tooltip="user.username"/>
-		<span class="username" v-if="showUsername">{{ user.username }}</span>
+			v-tooltip="user.getDisplayName()"/>
+		<span class="username" v-if="showUsername">{{ user.getDisplayName() }}</span>
 	</div>
 </template>