Replace <colgroup> and <thead> with bs4 tags

[munnsmunns]

Replaces use of the <thead> and <colgroup> html tags with the more condensed bs4 template tags where possible. Also replaces alerts with the bs4 alert tag where possible.

Notes:

• Alerts with additional css classes were left as-is since adding those classes would require changes to the bs4 function. You can find them by searching class="alert in the VSCode search.

[shapiromatron]

Nice job, I found a few more cleanups but looks good.