Port context to Drupal 8

I've started working on what could become context in Drupal 8. I've not made a port of the existing module bit instead I've created something from the ground up that leverages the way stuff is built with Drupal 8.

The work I've done so far can be seen over at Github, there's still a lot to do but the basics of the module is there with the entities and the forms.

Things to do and figure out:

• When during runtime execution should Context conditions be evaluated and reactions fired?
• How do you supply Drupal contexts to a Drupal condition during runtime?
• Context reactions are currently very simple Drupal plug-ins with forms. Do they need more abilities?
• Tests needs to be written?

I've done most of the work in my spare time so far but will also be working some with this during work hours.

Kindly copy any missing information to the original issue over at #2116959: Port context to Drupal 8. Thanks for working on this!