Set one makefile configuration as default

[andreeis]

Following up on the suggestion of #80.
It could be useful to add a field in makefile.configurations to make one configuration as default, to be picked whenever the project state doesn't seem to have recorded another selection previously.

[KrestenHelstrup]

@andreeis That is correctly understood.
If I want to open the project on another computer I would like to avoid the step of selecting configuration.