Representable variables

[felixchalumeau]

Inspired by #71 . In the same way that we can choose if a variable is branchable, it could be interesting to have the flexibility to choose if a variable should (or not) be added to the DefaultStateRepresentation.

Not a priority though.

[ilancoulon]

Hum, I would put it as a function defined in the default staterepresentation. Like a method that could take as an argument an array of variables we want to represent. I think this would be too specific to put in the addVariable function.

[felixchalumeau]

How, "inspired by #71" meant that this PR made it possible to choose but wasn't suggesting to implement it in the same way ;) Just saying it would be interesting to have the feature, not suggesting a way to do it ! Well, you're suggestion could be a nice way to do it though