* Always use cache: stop passing skipCache among ngalert functions
* Add updated column
* Scheduler initial draft
* Add retry on failure
* Allow settting/updating alert definition interval
Set default interval if no interval is provided during alert definition creation.
Keep existing alert definition interval if no interval is provided during alert definition update.
* Parameterise alerting.Ticker to run on custom interval
* Allow updating alert definition interval without having to provide the queries and expressions
* Add schedule tests
* Use xorm tags for having initialisms with consistent case in Go
* Add ability to pause/unpause the scheduler
* Add alert definition versioning
* Optimise scheduler to fetch alert definition only when it's necessary
* Change MySQL data column to mediumtext
* Delete alert definition versions
* Increase default scheduler interval to 10 seconds
* Fix setting OrgID on updates
* Add validation for alert definition name length
* Recreate tables
