Fix, be more generic

node.std_pos can’t be assumed, so one solution would be to be functor of the location attribute but it is not very useful anyway.
Fix node boundaries in clean_node

Before no assumption was made, but we know that nodes with children are of the width of them.
Remove unused CXX field from the language def.
Add a basic unit system. Use it for ‘time’ values.
Add preliminary radl__time user library
Some leftover tests
Correctly call subprocess with PWD updated

This allows among others catkin_make to work as expected.