Email templates are in HTML, but are not sent as HTML

The various email templates are in HTML files, but when they are sent, they are not sent in a way which that signals a receiving client to render them as HTML. There's also some code that pulls text out of <p> tags, which kind of undoes the HTML. See https://github.com/NUKnightLab/weatherbot/blob/54eefc2b1cc180aef13f2e160a2201a4ec3dbc2b/NHC.py#L322-L324

(I also wonder if the <ul> content of some email templates comes through that process looking as we'd like it to.)

We could change the templates to be plain text, although formatting lists in ASCII is a pain; or we could use more advanced methods of the python email.message library to send the email as HTML, which is a different kind of a pain.

But if we are sending the messages as text, we should use text templates, and not HTML templates with a custom process for reducing the templates to plain text.

Start with NHC.py at lines 322-324 and review how the HTML templates are converted before being sent. Read the Python email.message documentation to compare the available plain-text and HTML approaches. Done means the chosen message format is signaled correctly to receiving clients and list content renders or reads as intended.