Add icons to show message status

[Thalysonb]

I'd like to be able to see the status of the message, represented by an icon, on the screen. Something like:

These icons can be passed by parameters to ng-chat component, with the status type. I thought on something like this for example:

[ { status: 'sent', icon: 'icon_url' } ]

Also wold be nice if on this object we could pass an property to use when we need resend an message that was not sent, like on image above.

And finally, wold be nice if the library had a method to update the message history, to use when the message status change.