Validate event rule configuration #350
Description
At the moment, the form only relies on browser validation. select elements verify themselves already, but the number input does not. (Icinga/ipl-html#145)
If validation fails, the errors are not visible as the elements are currently not decorated. This should be done once Icinga/ipl-html#146 is merged.
Then there is the case of duplication. Duplicated conditions and recipients per escalation as well as entire duplicated escalations. Such should not be possible.