Be more compatible with Facebook emoticon codes

Since we support Facebook chat, and interoperate with the chat from the
browser, we need to support roughly the same emoticon codes.

https://bugzilla.gnome.org/show_bug.cgi?id=692689
EmpathySmileyManager: use the proper Unicode characters

For emoticons that are part of the freedesktop icon spec and of
Unicode 6.3, recognize the character and replace it with the icon.
Also, prefer the unicode character to the older ASCII encoding.
This ensures the maximum compatibility with Hangouts, and also
looks nice on iOS/Android.

https://bugzilla.gnome.org/show_bug.cgi?id=692689