Don't create reply message if operation is already defined by message view

[Matthias Schoettle]

Currently, when a new message is created and the signature returns anything except void (plus some extra constraints) it creates a reply message as well. However, in case this operation already has a message view defined it should not do so.

Furthermore, the UI then must allow to create new messages directly after the newly created message (in MessageViewView when determining whether message creation is allowed).

[Matthias Schoettle]

Resolved issue #221: Create messages are not created when a message view is already defined. This changes the state of the spacers on the lifelines on whether message creation is allowed, i.e., it is allowed directly after such a message call (on the send event side, not on the receiving end).

→ <<cset 0b1513b5e5de>>

[Matthias Schoettle]

References #221: Fixes expression from commit 0b1513b, such that message creation after a self-message that have a message view defined, are possible again.

→ <<cset 2140a33fe3e5>>