disable plugins from the backend

the installed plugins are tracked in the plugins table and have a flag to say if they are active or not. There is also the code to find active plugins vs inactive ones.

The Events system should use this to filter out calls to plugins that are not active. This will mean that its almost as if the plugin does not exist.

There are a few things that may cause issues like some of the plugins being bootstrapped before the models are loaded and the event system can actually check for anything that is active.