Make permutation sweep configurable

[sverhoeven]

In #72 a sweep button for permutation was introduced.

For now it is hardcoded to generate 24 permutations without any possibility for configuration. It would be nice if a user could pick the parameter, and choose sweep type with subform for

1. Start, end, number of steps. It would be nice if the start could be initially set to the default value+increment.
2. Start, increment, number of steps
3. Give list of numbers

Picking parameters could be done with

1. A form same a reference config edit, but with all text fields replaced by checkboxes. Selected parameters use field array to show a sweep subform.
2. A combo box, which is missing items already selected. Either selecting a parameter will add a new array item with a sweep subform. Or you have array item add button and each sweep subform has a parameter combobox.
3. A combo box, where you can select multiple. Each selected parameter has a sweep subform.

[sverhoeven]

It would also be nice if you could overwrite or append to existing permutations using a switch component.