[FEAT] Render Pool without boundary

[csouchet]

A Collaboration can contain two (2) or more Pools (i.e., Participants). However, a Process that represents the work performed from the point of view of the modeler or the modeler’s organization can be considered “internal” and is NOT REQUIRED to be surrounded by the boundary of the Pool, while the other Pools in the Diagram MUST have their boundary (see Figure 9.5).