Add horizontal scroll bar

[tpetricek]

For very long lines, we need to have a scroll-bar. For example: http://fssnip.net/rZ

[kunjee17]

@tpetricek horizontal scroll bar will going to hurt mobile view? You are talking about that only right?

[tpetricek]

The current display is broken even in non-mobile.

You can see that in the snippet, the line:

Chart.Geo(growth)
|> Chart.WithOptions(Options(colorAxis=ColorAxis(values=[| -100;0;100;200;1000 |], colors=[| "#77D53D";"#D1C855";"#E8A958";"#EA4C41";"#930700" |])))

Is too long, it breaks into two lines and, as a result, the code does not align correctly with line numbers.

So we need to fix this on both big and small screens.