Fixing resizing performance issue in split view 

Resizing in split view is too slow because the width of the codemirror editor is changing on resizing and it has to render it's contents every time.

We change the width to fixed size (3000px) on resizing start and restore to default at the end so codemirror doesn't render it's contents anymore :)
Great to see that you made lots of changes in JS. But you also need to have proper spacing in CSS. i.e we would like to see exactly one space before `{`, `!` and one space after every `:`,  and we don't want extra empty lines.