Updated to new upcoming Grav and $page references

Hey there,
just another heads up, we have merged our features into `develop`  and that required a small change in your plugin regarding the `Event` reference. We are now using a Toolbox external library.

While I was testing the plugin I also noticed that there were some issues with the way the page was get. I have updated the plugin to now pass the `$page` across all methods. During my tests it happened that in the `initConfig`, getting `$this->grav['page']` was too early and caused the headers to default to the Error 404 page.

This seems to be fine now but I couldn't get the unit tests to work, you might need to have a look at that.

Thank you!