Change to use first element as default for toggles

[djsegal]

Resolves:

• Way to switch to first option as default Interact.jl#247

See:

[piever]

I think this makes sense as it's the only option widget that starts in the middle rather than from the first element . Could you fix the tests on 0.6 ? I think there are some tests with togglebuttons that test the default value and are failing here.