Handling target=_blank if link points to a file

[AndrewR8]

Issue URL: #753

Steps to test this PR:

1. Navigate to http://www.granditaliaperth.co.uk/menus.html and click on the download link for the menu.
2. The download will start and a new blank tab closes immediately

[subsymbolic]

Many thanks for submitting this, we really appreciate it. Unfortunately an earlier PR #663 has now been merged and clashes with your approach. If you get up to speed with the develop branch you'll see that closing the extra tab also dismisses the new download confirmation dialog.

If you want to try implementing a different solution, you are most welcome to update this PR. If not, that's ok too, just close this PR.

[AndrewR8]

DownloadConfirmationFragment is attached to BrowserTabFragment. It looks like there are only two available solutions :

1. Attach DownloadConfirmationFragment to Activity (If empty tab should be closed)

2. Empty tab will be open until user dismisses DownloadConfirmationFragment

I need your advice.

[subsymbolic]

Solution 1 sounds good 👍

[AndrewR8]

I'll open a new one