Capture exception when petition creator is updated

When the creator's email address has also been used to sign the petition (e.g. a shared email address for a couple) then updating the name to match the other signature causes a not unique exception. Capture this exception and display it as a form error and not a 500 page.

Fix some minor admin bugs

• Fix race condition when two moderators go to edit a petition at the same time
• Restore tagged petitions to traffic light banners on admin hub
• Upgrade Appsignal and move admin requests to separate namespace

Fix a couple of bugs with petition edit locking

• Don't raise error on destroy if the lock isn't owned by us
• Use window.history.back() when a petition isn't moderated yet

Petitions re-opening September 2017

Merge pull request #622 from alphagov/deploy-after-archiving

Refactoring for re-opening

Update petition id sequence to start from 200000

Merge pull request #620 from alphagov/update-petition-ids-for-2017

Update petition id sequences for re-opening

1.3.0

Use simpler messaging - it's unlikely to be hours

Archiving petitions phase 3

The third release changes the application to use the new schema.

Archiving petitions phase 2

This second release adds the new schema and a migration task for copying the data from the old columns to the new tables.

Archiving petitions phase 1

This is the first release in a series of deployments to archive current petitions. Specifically, this release is to bring the display of archived petitions more in line with current petitions.

Maintenance rollup

Includes #584, #587, #588, #589, #591 and #592