Make the constructors uniform!

[luca-heltai]

Our constructors, derived from ParameterAcceptor, all take default values. Some of them take as default values the strings representing the values, some of them take as default values the actual values.

We should be consistent. Taking the strings makes one passage easier, but it increases the number of member variables for no reasons (the default value should be stored in the variable itself).

[luca-heltai]

Taking the strings makes one passage easier

This is no longer true. We should really remove all unneded strings.