Remove or refactor FormGroup

[matthew-white]

Our FormGroup component corresponds to the Bootstrap form-group class. It is used when a .form-group has a corresponding .form-label. The component also implements functionality around the form control.

FormGroup worked well when we only used simple input elements for the form control. However, we now use .form-group and .form-label together with select elements, as well as the flatpickr input. That means that there are a few situations in which .form-group must be used, but FormGroup cannot be, which seems potentially confusing.

We could consider refactoring FormGroup so that it works with a variety of form controls. However, FormGroup does relatively little work outside of the form control, so it may also make sense to remove the component and go back to just using .form-group outside a component.