Add the sleeping face into the Speak activity

[llaske]

In the Sugar version of Speak activity, there is a fun feature: after 2 mn without activity (not speaking), the face says he's sleepy then do a sleepy face. See screenshot below:

It could be nice to implement this feature.
The sentence "I'm sleepy" should be localized.
The sleepy face should be adapted to the number of eyes and eye form.
The source code of the Speak activity is located here: https://github.com/llaske/sugarizer/tree/dev/activities/Speak.activity

[llaske]

Fixed in #248