NLSR

Currently the LSA types mix logical const and non-const in their usage. This is a problem, because it makes reasoning about an LSA much harder, and reduces code hygeine. The LSA types should be const correct so that operator== can be implemented correctly, as well as improving design clarity.

This will probably require a rewrite of the LSA types, as the problematic underlying data structures differ from one to the next, and the ways they are modified are inconsistent.