change White guibg to compatible with macvim and some minor changes.

[xavierchow]

1. Since the default background of macvim is white, White without guibg is transparent and hard to be recognized.
2. Highlight Identifier(var,this) to Blue because I think they are import keywords in javascript.
3. Highlight braces which may helps to eliminate some typos.
4. The default color of javaScriptFuncExp( such as var myFunc = function(){...}) is rather harsh, I changed it to shallow pink.