Implement sharing calendars / task lists

[raimund-schluessler]

Implements a sharing menu in the calendar list. You can now share task lists with other users. Closes #14.

@skjnldsv I shamelessly copied most of the code from the Contacts app 😇 Works very good as far as I can tell.

Reviews very welcome!

[raimund-schluessler]

I will merge this now, so that the translations are getting updated. Reviews and testing is still welcome. If issues are found, we can fix them in later PRs.

[skjnldsv]

No issues found so far! Ui is good and works great!! 👍
Great job!! 😉

[marbetschar]

@raimund-schluessler not quite sure where to put this, so I shamelessly add it to your pull request here :)

Is it possible to share a public link for a task list? I've seen it's possible in the calendar UI, not sure if I'm missing something in the tasks app. The use case is: I'd love to invite some Non-Nextcloud users to a given task list where they at least can see what's on it using their favourite task-app (Apple Reminders, Web UI, or whatever...)

[raimund-schluessler]

@marbetschar No, this is not possible yet. I think this issue is tracked in #469. As a workaround you could maybe create a calendar in the Calendar app and publicly share the WebCal link from the Calendar app. Tasks should also show up the in their favourite task-app then (but I haven't tested this).

[marbetschar]

@raimund-schluessler understood. Thanks for clarification!