Add criticality the the tree selection algorithm as described in the [master's thesis of Petr Baudis](http://pasky.or.cz/go/prace.pdf) and in [this short presentation](https://github.com/ujh/iomrascalai/files/29566/Criticality.pdf) <!--- @huboard:{"order":210.271025,"milestone_order":210,"custom_state":""} -->
Add criticality the the tree selection algorithm as described in the master's thesis of Petr Baudis and in this short presentation