add different 'actor' drawing

[SebCanet]

Is your feature request related to a problem?

No

Describe the solution you'd like

Choose a different draw for actor, not only a human

Describe alternatives you've considered

Human and 'object', like a box in Magic Draw

I use Gaphor in a school, so we would to select between a human and a 'object' actor, to help students to create their own sysml diagrams.