Feature request: explicit order of lifelines

[dimaqq]

Let's say I wanted specific order of lifelines.
For now, I'm using these dummies @found statements to set it up

@found "1"
@found "2"
@found "3", ->
 @message "prepare", "2"
@found "1", ->
 @message "use", "2"

Of course there are display artefacts because of that...
It would be really cool if order could be set up without artefacts.