Rebuild/update all containers

As an administrator, when there is a big vulnerability that is patched in the OS images (like heartbleed), I want to update all my container images to include the fix.

I think there should be a button in the admin panel that says 'update all container images'. This would trigger a rebuild for all projects on the server.

/cc @ayufan @markpundsack @dzaporozhets @JobV

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