Don't require Frequency sorting dictionaries to be enabled when setting a Frequency sorting dictionary

[dgisser]

It's unintuitive that you can select a Frequency sorting dictionary in the dropdown but that's not sufficient to enable it. You also have to enable it like other dictionaries. The other dictionaries are included in vocabulary dropdown, not for frequency sorting, and this isn't mentioned explicitly in the current UI, making the behavior very unintuitive. I think if a dictionary is selected as a Frequency sorting dictionary, the user shouldn't need to also enable it.