NIAttributedLabel: Disable actionsheet for non-Internet URL’s

It was a problem that I saw when I was using - addLink:range: to create some internal links for in-app navigation.

I use some special URL scheme to distinguish internet URL's (Like we used to do in Three20, tt://someThing)

But NIAttributedLabel does not perform any checks before showing actionsheet (Open in Safari etc.)

For in-app links, the actionsheet firstly innecessary, secondly we would not want the user to see our internal URL (which is generally ugly)

This commits adds a check that performs a control. If the URL is an Internet URL (HTTP(s) or FTP). If not, does not show actionsheet.