This is done by using a zip file as backup. This includes both the YAML
data and a schema.rb. When restoring, we create an empty database using
the schema.rb, import the data, and then run all the pending migrations.
This feature has been backported from master. It includes adding the
yaml_db gem which is wrongly in #52229b87 on master. It also includes the
tenants/form refactoring from #b8e3273e which refactored for the setup