Provide turn angle distributions from experiments

[mastrof]

Some classical turn angle distributions should be made available, e.g.:

• E. coli as measured by Berg & Brown, PNAS 1972 (Fig. 3)

A convenient implementation could be obtained by finding an appropriate analytical distribution in Distributions.jl, eventually also using a MixtureModel if the distribution has to be extended from [0,pi] to [-pi,pi]