Add reinstate feature for deleted files

- Add MarkNotDeleted method to repository
- Add ReinstateFile method to service
- Add AdminReinstate handler
- Add /reinstate/:id route
- Add Reinstate button in admin menu for deleted files

templates/admin.html

@@ -183,6 +183,10 @@
                         <form action="/api/files/admin/delete/{{.ID}}" method="GET" onsubmit="return openConfirm(event, 'TERMINATE', 'Kill this file? It will be removed from active storage.')">
                             <button type="submit" style="background: #ffcccc;">Terminate</button>
                         </form>
+                        {{else}}
+                        <form action="/api/files/admin/reinstate/{{.ID}}" method="GET" onsubmit="return openConfirm(event, 'REINSTATE', 'Restore this file to active status?')">
+                            <button type="submit" style="background: #ccffcc;">Reinstate</button>
+                        </form>
                         {{end}}
                         <form action="/api/files/admin/delete/fr/{{.ID}}" method="GET" onsubmit="return openConfirm(event, 'FULL_WIPE', 'Wiping file and purging record? This is a permanent database scrub.')">
                             <button type="submit">Full_Wipe</button>