add feature to insert container with chosen before target <select />

In our project we have to have ability to move chosen div container before target `<select/>`, because other api functions may insert elements just after  `<select/>`. And this might break design flow.

So, demo follows:
`$('form select').chosen({insert_before:true});`
- if you set "insert_before" option to true, then container will be before-ed to `<select/>`

Thanks