Added a showCancel option to explicitly remove cancel button if wished

[ConcurrentHashMap]

I needed some confirm dialogs for a customers project, where the customer only wanted to show up a "OK" button as the information was just "read this and then go ahead", so that showing up a cancel button would only confuse users.

So this is what I changed. The changes should be completely compatible with the current implementation, as the button will only be hidden, if showCancel is explicitly set and evaluates to false.

Hope this will help some others too.

[jameskleeh]

So I think if you want to deviate from the standard template structure, you should simply provide your own template. We could add settings like this for every piece of DOM there and it wouldn't be pretty.