Updated filtertools.initial_gaussian_params
Updated filtertools.initial_gaussian_params

Found a bug where the initialization for ft.fit_ellipse was leading to
poor initializations for some STAs, leading to incorrect ellipse
coordinates. This implements a simpler (and hopefully more robust)
way of estimating the initial parameters of the 2D gaussian to fit in
fit_ellipse (the xy center and the precision matrix)

baccuslab/pyret