Clean selections when state is removed
Handle style changes properly in token
VERY dubious bug - watch out for this

A token can be undefined in the token directive - it's not really clear
who makes such a cool. We have to search for this carefully - could be
a leak.
Create head watches on the fly in dependency Tree

When the tokens change, we need to update our watches, otherwise we'll
see no movement in out tree once we navigate to a new sentence.