Drupal 8 port

I just pushed a first version into an 8.x-1.x branch, figured that a patch or so wouldn't be too useful.

I started with running it through drupalmoduleupgrader, which did a lot of the basic stuff like routes, permissions and moving things into forms/controllers.

I didn't do a lot of testing yet, but I've a) implemented a adapter service, so that we can abstract all the different function_exists/extension_loaded checks, and this will also allow to write a test implementations that stores things in state or unit tests.

Exception and watchdog handling has been converted, but is completely untested.

I rewrote the ignore/background stuff into a request listener that runs after the router. The reason for that is that I additionally implemented a feature that sets the transaction name to the route name. New relic tries to support Drupal8 but it a) reports a lot of weird things (most transactions are named after a random (?) pre_render method) and b) uses the Controller name, and I think using the route name is much better for views and generic entity/form controllers.

Deployments/reports hasn't been updated yet.