Improve plugin hook cyclic detection

[WithoutPants]

From Discord:

I can see you have blocked the events being fired if your plugin schedules the scan task to prevent plugins being called again and again recursively but i'm doing it in a way that should not cause problems.

This PR addresses this issue by making the plugin hook cyclic detection a bit smarter. It now records the plugin and hook type data, and allows up to ten of the same hook type before cutting off. Ten is an arbitrary number that should not generally be hit under normal circumstances.

Also moves and renames plugin.HookTriggerEnum to hook.TriggerEnum - in a package underneath plugin.