Allow to select aspect message views from extended aspects

[Matthias Schoettle]

Problem: When specifying "affected by" for message views, aspect message views from extended aspects cannot be selected.

Steps to reproduce:

1. Create a "conflict resolution" aspect that extends Ordered and Unique of Association
2. Try to select the checkUnique aspect message view from Unique in a message view

Because this happens within a concern (and a concern designer is responsible for it), it should be possible to do so and avoid having to duplicate aspect message views, i.e., it should be possible to reuse them.

[Matthias Schoettle]

Resolves #301: Adds aspect message views from extended aspects to the choice of values of the "affected by" property descriptor.

→ <<cset a4413083aabf>>

[Matthias Schoettle]

References #301: Bug fix: Adds back aspect message views of current aspect.

refs #373

→ <<cset a821fd2417b4>>