Grid view features

Hi there,

at work we're using riemann and riemann-dash to monitor our production environment.

Having lots of metrics to keep an eye on, we found useful the possibility to scroll each Grid view independently in a single tab. Furthermore, sometimes it could be more effective organizing the Grid for having metrics in rows instead of hosts.

In the code I added

    overflow: auto; 

to `grid` class in the stylesheet and a `transpose` field, in `grid.js`.