Provide richer information when using NSSharingService

[barijaona]

Provide title of article in addition to URL
Title is used as sharing service's subject

Unfortunately, NSSharingService is not yet smart enough to pass multiple types of content.

Fix issue #1678

[Eitot]

It seems that this breaks adding an article to Safari Reading List.

[Eitot]

It seems that NSSharingService simply picks the first result of [Article writableTypesForPasteboard:]. Presently it returns NSPasteboardTypeRTF which works for Mail, but not Safari Reading List. When switching to NSPasteboardTypeURL, Safari Reading List will work but Mail will only share a URL.

[barijaona]

It seems that this breaks adding an article to Safari Reading List.

I see in the log:

[NSExtension] Extension request contains input items but the extension point does not specify a set of allowed payload classes. The extension point's NSExtensionContext subclass must implement `+_allowedItemPayloadClasses`. This must return the set of allowed NSExtensionItem payload classes. In future, this request will fail with an error.

This warning also appears when I use the 'Email link' menu item…
But it does not appear when I use the Share icon and select Mail ?

[barijaona]

OK, I don't want to fight what appears to be AppKit bugs on NSSharingServicePicker and NSPasteboardWriting and will revert to a less sophisticated approach.

[Eitot]

Looks good to me otherwise. I prefer the narrower scope of the PR without the pasteboard stuff. NSPasteboardWriting has to be done eventually, but it has some annoying pitfalls.