Fix issue #17: Fix problem with radical as image for quiz
Use mutation observers instead of mutation events

(for the note updated detection)
Issue #9: Use mutation observer instead of waitForKeyElements for quiz mode.

Lessons are still using waitForKeyElements, so that needs to be addressed
separately.
Fix issues #9, #16: Use Mutation Obersvers instead of waitForKeyElements

With this it's also possible to get rid of attrchange and jQuery
dependency.
Get rid of eval()

Trade compact code that uses eval() for eval() free code that
is more readable and grep-able
Drop support for http since WaniKani now forces https
Update version to 1.8