Fix refresh and use directive argument as slimScroll option. 

Things in this PR. 

1. Fix refresh by adding option eval and destroy slimScroll before recreate.
2. Allow slimScroll option to be specified as directive argument. Syntax: `slimscroll="slimscrollOption"`.
3. Watch on directive argument option, unless `noWatch: true` option has been specified.

Let me know what you think.