Task Notes as Markdown

The current angularUI Bootstrap doesn't support custom templates nor the ability to set HTML as Content, thats why I had to add this: http://stackoverflow.com/questions/23406357/extending-angular-ui-bootstrap-popover/23409972#23409972

And I had to add some model input debounce too, so that the marked text won't be generated on EVERY keydown, which slowed (here) down everything: http://stackoverflow.com/questions/15304562/how-to-put-a-delay-on-angularjs-instant-search/18494567#18494567

This Pullrequest needs: habitrpg/habitrpg-shared#318

Once merged this Issue can be closed too: #3508