Allow user to make charts bigger

[MyForest]

When doing analysis over a long period of time it's nice to be able to see the graphs in a wider format.

At the moment the content container is restraining the graphs to 1150px.

[MyForest]

By removing the max-width the rest of the layout grows to use the space.

With flot doing the redraw on resize we now get reasonable re-fills of the space.

[MyForest]

The downside of this solution is that it's overriding the CSS for .content-container from the Emoncms stylesheet, but that was hard-coded to 1150px which was very limiting on a 4k monitor.