Fix devtools Profiler in safari

 - Use [https://github.com/postcss/autoprefixer] to add prefixed CSS directives needed for browsers like Safari or IE.
 - Fix SplitView pane to update prefixed CSS directives too

Note: this patch fixes the CSS-related issues, see #844 for a list of other issues.

/to @anthonyettinger please review
/cc @seanbrookes @rmg