Fixed `margin-bottom` and Class Encapsulated Quickdraft

Based on what @growthdesigner said I fixed the CSS file; I got the 2.1.1 version of MP6 and still got the error (Mac OS X, Chrome).

Even if MP6 address this problem I think we should have a fix on wp-dash.

No `!important`by the way.

Then I've did what @danielbachhuber commented on the #7, encapsulating a Widget in to Class; But I'm not sure if choosen a good name since there are some `dash_ ` and some `dashboard_`