[PROPOSAL] Add force parameter to Graph add... functions

[Grufoony]

The way one assing ids for both nodes and streets is not so clear... if you modify a lot your network you have to call many times buildAdj() function and others.
To avoid this we could ask whenever to force the insertion of an element.
For example adding a street may become something like:

void addStreet(const Street<Id, Size>& street, bool bForce = false);

When called with the bForce false, it automatically reassigns the id and does any other operation buildAdj would do.
If called with the "forced" version we can assume the user is telling us "Come on, I know what I'm doing", and keep the current behavior.

What do you think @sbaldu @filippodll?