Mirror.interval column type needed to be changed to bigint.
Correct interval where the interval set is < MinInterval.

* Sync interval specifed as duration string

* Changed mirror interval text

* make fmt

* Add MinInterval for mirror sync

* Use duration internally

* Changed min default to 10m

* make fmt

* Incorrect default

* Removed defaults in MustDuration()

* Add Mirror interval migration

* Default values corrected

* Use transaction during migration

* Change http 500 to page with error message

* Cleanup session.commit()