Without system cron: warning and a backup that moves on while the page is open (#13); progress of the database phase; Bin tab

- The admin page and backup:status warn when background jobs do not run on a
  system cron, or the cron stopped, with a link to how to set one up.
- Without a working system cron, the open admin page moves a running backup
  forward through /api/tick, a short step per poll.
- The database phase shows the tables dumped ("db: 47/183 tables"); a backup
  that has not moved for 15 minutes says it is waiting for background jobs.
- The trash of restore points is on a tab of its own, Bin.
- New screenshots; changelog and plan for 1.0.2.

src/api.js

@@ -33,6 +33,7 @@ export default {
 	testTarget: (id) => call('post', `/targets/${id}/test`),
 	setTargetLimit: (id, maxGb) => call('put', `/targets/${id}/limit`, { maxGb }),
 	startBackup: (targetId, label) => call('post', '/backups', { targetId, label }),
+	tick: () => call('post', '/tick'),
 	setSchedule: (time, timezone) => call('put', '/schedule', { time, timezone }),
 	snapshots: (targetId) => call('get', `/targets/${targetId}/snapshots`),
 	browse: (targetId, snapshotId, path) => call('get', `/targets/${targetId}/snapshots/${snapshotId}/browse`, { path }),