Pks+as/expiration enabled events

handles #31 

#### Adds two ways to disable submission
_thanks to @gruntrebel_

- Events can be set active or inactive
- Events can be given an optional expiration date
  - Optional state provided by presence of a date or nil in the expires property

##### Extra things you will see
- The control list will clue you in on that state at a glance

##### Also blocks submission by URL hacking
- Makes sure an event is active before you can access the new action