Overview mockup

First mockup of overview where tasks/builds will be displayed.

I named them "Tasks" in order to not get too stuck into the builds terminology. Perhaps we want to display different type of things here, and naming it appropriately from the start might help with that.

Things I want to get done in this PR:

- [x] Make a default template (can be ugly, but should catch the idea of what the overview might look like)
- [x] Basic model for the `Task` collection. What data might we need here?