[Direct Edition:002]: Message label

It SHALL be possible to edit the label of a message directly in the diagram.

The editor SHALL provide content assistance and autocomplete support for:
- The message name matching na operation or signal provided by the receivinglifeline.
- The name of the argument matching an operation parameter or a signal attribute
- The wildcarded value when applicable
- The possible values of the arguments (lifeline context property, interaction parameters, constant values, etc...)
- The possible assignment targets
- Return values: the editor then SHALL populate the message signature, message arguments, and
its value specifications.