resizeFromBody, filenames

I fixed your file naming convention. There was an issue when running grunt because `jquery.resizableColumns.js` was named `jquery.ResizableColumns.js`. 

I also added a `resizeFromBody` option that defaults to true. I wanted to restrict resizing of the table to just the header (`thead`). So setting `resizeFromBody` to false will restrict it to within the header. There is probably a better name for the option.