Have some property to detect and use the current term

[jonespm]

We have CANVAS_TERM_IDS for specific terms. It seems like it would be useful to have the code be able to detect the current term so we don't have to update this each year.

If this CANVAS_TERM_ISD is empty then just have it detect what the current term is.

I'm not 100% how this would be done since the date end date is extended off into the future, so we'll have to just use the term that has a start date before today.