Fix problem that override options for footer, and others

Right now if you apply a className like below:
```javascript
var Footer = Backgrid.Footer.extend({
  className: "FooterClass",
  tagName: "tfoot",
});

var grid = new Backgrid.Grid({
  className: 'MyTableClass',
  columns: columns,
  collection: collection,
  footer: Footer
});
```
It will create this HTML
```html
<table class="MyTableClass">
  <thead class="MyTableClass">
  <tfoot class"MyTableClass">
  <tbody class="MyTableClass">
```


This change pass only the required columns and collection options to Footer, Body and Header, so other options like className won't be overridden.