Ensure that spec names describe their intent

There are several spec files whose name doesn't reflect what they are trying to describe. Instead, they refer to sections of the example website where the spec'd behaviour happens to take place.

For example:

• spec/features/log_entries_form_spec.rb describes select fields.
• spec/features/line_items_spec.rb describes index, edit, and new pages.
• spec/features/orders_form_spec.rb describes select fields (again), belongs_to associations, has_many associations, and datetime fields.

As a result, sometimes I find myself looking for a spec example and not remembering where to find it.

We should reorganise these specs so that they refer to the functionality that they are describing.