feat(tasks): make done at column available for selection in table view

This change adds the done at column of tasks to the table view. It also ensures it is possible to sort the tasks by that column.

https://community.vikunja.io/t/is-it-possible-to-list-done-tasks-with-their-completion-date/1922

frontend/src/views/project/ProjectTable.vue

@@ -52,6 +52,9 @@
 								<Fancycheckbox v-model="activeColumns.percentDone">
 									{{ $t('task.attributes.percentDone') }}
 								</Fancycheckbox>
+								<Fancycheckbox v-model="activeColumns.doneAt">
+									{{ $t('task.attributes.doneAt') }}
+								</Fancycheckbox>
 								<Fancycheckbox v-model="activeColumns.created">
 									{{ $t('task.attributes.created') }}
 								</Fancycheckbox>
@@ -144,6 +147,13 @@
 											@click="sort('percent_done')"
 										/>
 									</th>
+									<th v-if="activeColumns.doneAt">
+										{{ $t('task.attributes.doneAt') }}
+										<Sort
+											:order="sortBy.done_at"
+											@click="sort('done_at')"
+										/>
+									</th>
 									<th v-if="activeColumns.created">
 										{{ $t('task.attributes.created') }}
 										<Sort
@@ -223,6 +233,10 @@
 									<td v-if="activeColumns.percentDone">
 										{{ t.percentDone * 100 }}%
 									</td>
+									<DateTableCell
+										v-if="activeColumns.doneAt"
+										:date="t.doneAt"
+									/>
 									<DateTableCell
 										v-if="activeColumns.created"
 										:date="t.created"
@@ -297,6 +311,7 @@ const ACTIVE_COLUMNS_DEFAULT = {
 	created: false,
 	updated: false,
 	createdBy: false,
+	doneAt: false,
 }
 
 const SORT_BY_DEFAULT: SortBy = {