Allow entering of email addresses in autosuggest

- [ ] It should be possible to add an arbitrary email address to the autosuggest component. This should only be allowed when a valid email is entered and the user hits enter. This should just generate an autosuggest item that contains the email address.
- [ ] The placeholder text should read "Enter people, groups and email addresses"
I think it would be a good idea to allow commas, but only when the entered text is a valid email address. Otherwise, the comma should just be used as is. That will remove the scenario where you search for a group with a comma in the name.