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"
It seems like having an empty "No results" message really is the issue. It's true that currently an empty message only occurs when we're allowing email, but that could change if we add another case where there is an empty message.

This code is adding a hook for CSS. The problem the corresponding CSS rules fix is when there is an empty message. Without the extra rules, the plugin still displays a (slim) message container even when there is nothing in the container.

![safariscreensnapz001](https://cloud.githubusercontent.com/assets/1731910/4646263/c4db3150-5471-11e4-9e68-66e3b10e4a13.png)