Gaia Sky 3.5.0-RC6

Features

add eclipses by projecting the shadow umbra and penumbra from moons to planets and vice-versa. The option to outline the umbra and penumbra is given as a checkbox in the preferences. Eclipses can be deactivated, also from the preferences window, graphics tab.
dim atmosphere w.r.t. camera, star and eclipsing body positions during eclipses.
use coordinates provider from objects to sample periodic orbits instead of hardcoded algorithms.
add support for VSOP2000.
initial support for ephemeris based on Chebyshev polynomials.
add a few showcase scripts

orientation locking does not work in backwards time. Fixes #718.
bump default safe mode OpenGL version to 3.3 to support instancing. GPUs from 2007 support it, so it should be safe. Also, do not attempt to compile double-precision geometry shaders in safe mode, since they are not used and may crash anyways.
line trail mapping in non-timestamped trajectories. Fixes #715.
double-rebuilding of dataset manager on close. Also, closing the dataset manager does not persist the preferences.
shader version for normal shader from 410 to 330 to prevent crashes in old GPUs.