Fix the description box when changing to a feature type with no template

When changing the feature type to one that does not have a template, it no longer removes the last template from the description box. This used to work, but has been broken for months.

The box has to be wiped as well as changing the styling option away from H4 - which is typically the starting styling on the templates we see. That second step in particular is easy to forget, until you start typing a sentence and it's huge.

When a feature type selection does not have a pre-defined template, clear the description box and reset the styling to paragraph.