Display rationale text on check-results page

[felipesanches]

It seems that a large number of users have been using the dashboard web interface instead of running Font Bakery on the command line. One of the things that the command line displays but the dashboard currently doesn't are the blocks of rationale-text explaining the reasoning behind each check. This is extremely useful info to help the users figure out what's going on and, for that reason, it should be displayed on the web interface as well.