Icons for design roles

**What do you want to see?**
The player should be able to assign icons (not necessarily ICO files, just graphics in general) to design roles, and the default design roles should have icons.

**How would it help players?**
We can then use these icons in, for instance, the list of ships in a fleet - giving an overview of the fleet's composition by ship count or tonnage.

**Alternatives**
Abbreviations like SE2 had?

**Screenshots and mockups**
N/A

**Things to consider**
Where will player assigned icons be stored?