std::pair's to structures

I've replaced std::pair&lt;NodeID, NodeID&gt; and std::pair&lt;NodeID, bool&gt; with structs RestrictionSource and RestrictionTarget. I think now it's more readable and easier to understand.
Also replaced wrong type in CheckForEmanatingIsOnlyTurn method (in 'for' was RestrictionSource instead of RestrictionTarget).
The initialization should be done as before with curly braces.