Make warp point exits their own stellar object

**What do you want to see?**
Warp point exits should appear on the system map.

**How would it help players?**
You can see where warp points lead, in case they are one way. Will also speed up pathfinding because we will no longer have to scan the entire galaxy for warp point exits.

**Alternatives**
N/A

**Screenshots and mockups**
N/A

**Things to consider**
Should you see an incoming warp point before you warp through the corresponding outgoing warp point?

Warp point exits will also need to be destroyed when closing a warp point.

We will need graphics for these exits that is distinct from the regular warp point graphics.