[Merge] lp:~uriboni/webbrowser-app/undo-close-tab into lp:webbrowser-app

[Ugo Riboni]

Note: in the bug report both CTRL+SHIFT+T (as firefox and chrome do) and CTRL+SHIFT+W (to complement CTRL+W to close a tab) were suggested as shortcuts. I implemented both because I think they both make sense.
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https://code.launchpad.net/~uriboni/webbrowser-app/undo-close-tab/+merge/275849
Your team Ubuntu Phablet Team is requested to review the proposed merge of lp:~uriboni/webbrowser-app/undo-close-tab into lp:webbrowser-app.