Add option to enable rails csrf, copy ng-model values to input values

#### Add Rails' CSRF support

Added an option `enableRailsCsrf` to the `ng-upload` directive that enables passing the CSRF param to Rails.

    <form ng-upload upload-options-enable-rails-csrf>

Nothing fancy, just adds a hidden input to the form with the values of the Rails' meta csrf.

#### Copy the eval of `ng-model` to input's value

So I may be missing something, but the `ng-model` attribute on an input will never be passed since the form is simply being submitted and not being handle by Angular. To get around this, before the form is submitted, the value of the `ng-model` for each input is evaled and set as the value attribute for that input.