Multiple pyr_best_dens in a single array

[c0gent]

Create a single array of u8 to hold best_den_id. There's no need to handle more than 256 dendrites as this gives us a total possible 65k synapses. The array will be pyrs.len * best_dens_tracked (which will start at 3) in length.

No need to store the state for any of them. Pyr_states will be equivalent to best_den_0.

Give dendrites a learning bias based on their rank. best_den[0] >> 0, best_den[1] >> 1, etc.