Feature: copy to clipboard

There should be a button to copy the article contents to the clipboard.

UI:

• It should not have any language associated with it, so that it works in all languages.
• Using the model established by @mathieu-william, it should be a button next to the others.

Code:

• It should work on pretty much any browser possible, including older ones.
• If it won't work on a particular browser, the button should not be shown.
• There doesn't have to be visual feedback that the copy worked, but it would not be a bad thing.