No custom field 'catch all' group on a clean instance

[steveyken]

When a clean FFCRM instance is created (or demo data loaded), there is no generic custom field group that contains all the custom fields that do not belong in a group. As a result, these fields are not displayed.

We need to come up with a better solution - say if a custom field is not in a field group then it is just shown by default.

[steveyken]

Moreover, when the server starts, it will fail if there are custom fields not in field groups.

`rescue in klass': Field#klass delegated to field_group.klass, but field_group is nil:

[steveyken]

5f2795c is part of this

[steveyken]

Server no longer fails to start (see a0d9060 and ddeb731) but the core issue still exists.