Plugin could be half-activated, due to secret's absence, but Events Store would still capture data. As the rest of the plugin, notably its CLI commands, aren't loaded, this could store data into an unreachable hole. Also, with the introduction of a custom table, the table shouldn't be created when the environment isn't ready.

With unique constraints, this will help with situations where events with specific timestamps are changed

Looped until circuit breaker tripped because `$page` wasn't respected. Also revealed that an additional query was run when we knew it wasn't needed, because we got back fewer entries than we asked for.

When events are cleared with `wp_clear_scheduled_hook()`, they can't be rescheduled until the cleanup job runs.

Fixes #91

Fixes #90

CLI may use this eventually

`get_event()` method was removed earlier

Considerable cleanup and simplification along the way

This logic became spread across various classes during initial development, and it's time to consolidate.