Integrated several improvements from the Firefox version

* Single code-base will now work in both Chrome and Firefox.
* Made creation of DOM nodes slightly safer (no unescaped strings, uses more jQuery templating).
* Performance improvements: removed DOM modification listeners and replaced them with MutationObservers. More info here: https://developer.mozilla.org/en-US/docs/XUL/School_tutorial/Appendix_F:_Monitoring_DOM_changes?redirectlocale=en-US&redirectslug=XUL_School%2FAppendix_F%3A_Monitoring_DOM_changes
* Integrated optional Burndown Charts.
* Added debouncing of refreshList so that it never gets called too-frequently which could occasionally cause performance slowdowns.