Issue/360 check caption language

[atarisafari]

Fixes #360

[bagofarms]

My manual tests did not completely pass. While it was successful in detecting a mismatch in language, there is a major edge case that needs to be addressed. YouTube seems to use non-standard language codes for dialects. For example, a video from Univision will have captions with the language code es-MX for "Spanish (Mexico)". Example: https://www.youtube.com/watch?v=FcnrUf35LmQ

Since there could be tons of dialects for languages, maybe the best approach would be to only look at the first two characters of the language that YouTube reports back.

[atarisafari]

Upgraded feature to not rely on config variables. Now just checks for the Canvas course language without any need for user setup.

[atarisafari]

Note: Remind users in release notes that dialects will be treated as being the same language

[bagofarms]

I did some testing and found that way more YouTube API requests were being made than expected. I also talked to Matt about how we might be able to eliminate the extra API call for language by combining the two errors together and recognizing which one is which during the report building stage.