add (hidden) support for opening urls in tabs

[errantmind]

As it has been so long since this feature was requested, I figured I'd add simple support as a hidden feature, then @alct can style it in the UX at a later date if desired. This addresses #11

Flow:

1. User pastes text containing urls into the text area
2. User clicks the counter
3. Tabs open

Note, I don't see any UX issues with this, aside from it being a hidden feature. When the tabs open, the textarea automatically updates with the correct list of urls again, so this simple addition 'just works'

[adamency]

@alct Can you please just accept this PR ? I guess you don't have time to work on this project anymore, but it's a matter of 5 minutes to review the code and merge it, while it would add the most requested feature for this project. I would be extremely grateful.