Add Labels to PPC Options

[ghedlund]

Add grouping labels to make the PPC options more readable. As below:

General:

        ❑ Percent phones correct

        ❑ Percent consonants correct

        ❑ Percent vowels correct

        ❑ Percent correct (custom)

Syllable positions:

        ❑ Percent onset consonants correct

        ❑ Percent coda consonants correct

        ❑ Percent nucleus phones correct

               ❑ Dynamic options for syllable positions here

Singletons and clusters:

        ❑ Percent singleton consonants correct

        ❑ Percent cluster consonants correct

                 ❑ dynamic options for singleton/cluster group here

[ghedlund]

Placing the dynamic options in between radio buttons would require that each group is a single PhonScript parameter and that some link could be created between button groups to ensure only one item is selected.