o-ft-forms now uses o-ft-typography for Label and Additional Info styles

Unfortunately it's still directly dependent on `o-fonts`, as _prefix_, _input text_ and _error text_ styles are not yet in `o-ft-typography`. I'll speak to @pauloneillft about that.

Now calls `oFtTypographyIncludeFont(label)` instead of calling the `o-fonts` mixin directly (another step towards removing the dependency on `o-fonts` directly).

Other changes not directly related to this work:

* Renamed global-errors mustache template to match output demo name.
* It seemed that rendering in IE8 (and probably 7) was broken for checkboxes and radios. I haven't fixed that, but it's no worse after these changes. Shall I raise an issue, or is it in hand?
* Wrapped the first global-errors demo in a `fieldset` to be consistent with the demo next to it.
* Checkbox and radio demos have elements already checked.

@natashabryony @jamesnicholls @Thurst-ft please review. Thanks