Implement conditionnal traits for parametrized types

[samsa1]

Some parametrized structure might depend on the fact that the parameter has certain traits to implement it.

For exemple Vec<T> implements the traits clone or display only if T has this trait.

This feature would mainly needs to be done in typing/context.rs

[samsa1]

First of all, parametrized types should be implemented

[samsa1]

Trait system has changed a lot, currently it might be much easier to implement. However parametrized types should still be implemented.