Electron: Updates for Electron 1.2.8

[feross]

Followup PR to #738.

• Electron: Use default labels and accelerators
• macOS: add missing Edit menu roles
• Use 'quit' role
• Linux: Support showing badge count

Please review: @mathiasvr

[mathiasvr]

LGTM 👍
But I think the undo/redo menu items are a little confusing. They are always active even though there is nothing to undo/redo, and they cannot be used to undo something like removing or adding a torrent. Can they actually be used for anything else than undoing/redoing text in the Open Torrent Address modal? If not, I would remove them.

Edit: Just realized that this applies to Cut, Copy, Delete and Select All as well! Maybe it is obvious that these items only applies to text, In that case we could keep them, but I would separate the Paste Torrent Address item.

[feross]

We also have Cut/Copy/Select All which have the same problem.

It seems like most macOS apps tend to include these items even when they do nothing most of the time, so they can be used in text fields. I agree with you though. We should look at how we can disable these items when the user's not focused in a text field.