astro/stellarium: the port had been updated and improved (+)

- Update Stellarium to the latest version 0.22.0
- Introduce WEBENGINE option: it helps to query various websites such
  as Wikipedia, VSX AAVSO, GCVS SAI, etc. for extra information about
  selected object and display it in the plugin's window
- Because of the above, reword MORE_STARS option description to avoid
  using the word `extra' twice in the option selection dialog