Resolve "Date input for template lists"

Currently, a “Function” or “Class” template dance list without a date causes the “enter date” modal to be displayed when the list detail page is opened. Presumably a template shouldn't be associated with a fixed date, and so the dialog doesn't make much sense in this situation.

The obvious fix is to check whether a “Function” or “Class” list without a date is actually a template, and to refrain from displaying the popup in that case.

Closes #37 (closed)