Add toasts where sensible

[sorenjohanson]

Proposed feature In #284, we've added the ngx-toastr package to display a toast when successfully duplicating a mindmap. We should check where else toasts are sensible and add them.

[JannikStreek]

I would suggest to add toasts on all actions where it is currently not really clear that something happened. Two ideas at least:

• When the share url copy button is pressed inside the share modal. Currently only the url is highlighted.
• When the copy node button is pressed.
• After deleting a map, currently the browser is only redirected to the start page. Would be nice to see on the start page (so after redirect) "successfully deleted map"
• I would also propose to change the current notification for the duplicate workflow: Show the message on the new map, not on the old one. Instead of the timeout, redirect and use a query parameter to show the message