Better autosave error handling

[Janisvb]

At the moment, the autosave operation seem to ignore all errors and doesn't warn the user when there are any issues. This could lead to a loss of data in different situations, for example:

• the users internet connection drops, the user doesn't notice and continues writing -> no warning and data loss
• the backend throws an error while saving the changes -> no warning and the user would probably not see that the changes were not saved

I would suggest

• warn the user if there are any unsaved changes (same behaviour as without autosave)
• show any error from the api as a toast notification