[Code] Do we really need Utils::Bitset?

[rturrado]

Utils::Bitset may be a bit faster than std::bitset, but I don't see that's strong enough a reason to have this code.
We could use boost::dynamic_bitset, as we are already doing for BitRegisterMeasurement.
So a BasisVector would become a boost::dynamic_bitset<uint8_t>.
The fact that we could define these basis vectors with dynamic size could avoid doing some substring work (in order to reduce from the static 64-bit basis vector, the biggest allowed, to the n-bit basis vector, the one managed by a QuantumState).