Issue/713 Allows pasting URLs from Safari into the visual editor

[frosty]

Fixes #713. Links copied from Safari are only available with the text/uri-list content type, and we were only checking for plain/text. I've updated the paste event handling code to check for links before falling back to plain text.

To Test:

• Visit a web page in mobile Safari, and choose the 'share' action button. Tap "Copy", and then attempt to paste that link into the editor. Without this fix, it would fail silently. With the fix, you should see the link appear.
• Also test copying links from Safari by long pressing on a link and choosing copy.

Needs Review: @SergioEstevao (cc @kwonye)

[SergioEstevao]

@frosty should the links when pasted on the editor show up as links? or they just show has plain text in the editor?

[frosty]

I was wondering that myself. I think plain text is probably the right choice, for a couple of reasons:

• If you want a link, you can tap the link button. It will automatically use the URL on the clipboard if one is there.
• If you want to e.g. embed a YouTube video, you just want to paste the raw URL into the post (not a link)

[SergioEstevao]

:shipit: