Add method to reset file input and show file size and image/video/audio preview

[alejsanc]

If you fill out a text entry and later regret it, you can delete what you wrote. If you select a file then you cannot leave that input empty, you can only select another file. The file input should be able to have a small button to clear the field.

Other useful things would be to show the size of the selected file and a small preview if it is an image/video/audio

<input type="file" clear-button show-size show-preview />