[Front] Add lazy-loading to the family list, so it appears to load quickly

[felipesanches]

Originally submitted at https://github.com/googlefonts/fontbakery/issues/1282

We're now dealing with almost a thousand font families. This is too much to show at once at the dashboard front page, so it would be good to add a pagination system to show just a few families per page. Maybe 50 or so...

@davelab6 said: "The webapp still available from http://fontbakery.com dealt with this already, with some nice lazy-loading code. I hope you can use it :)"