Log Message:
stellarium: updated to 0.21.0

v0.21.0:
The major changes of this version:

We have finally completed our work on accurate planet axes, including Lunar libration
Visualisation of Earth shadow for Lunar eclipses
Better texture for the Lunar surface
Added the latest algorithms for planet magnitudes
Enhanced Calendars plugin
Replaced "arabic" by more accurate "al-Sufi" skyculture
Planets are now scalable and Solar glare switchable for didactic applications