COO creation

[gouarin]

Two types of creation will be needed:

• insert the element in a sorted way
• insert the element by adding them at the end of a container and sort them when the insertion process is done

[JohanMabille]

The first one is implemented in xcoo_scheme.

We can implement a coo_builder for the second one, that will sort its entries at the end of the creation process and return a sorted xcoo_scheme.