Remove or refactor FormGroup

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.