GEFS 1.2c

A new release to properly wrap up the migration to CesiumJS:

- Reworked all the 3D models to make sure they look good in CesiumJS
- Removed the last dependency to plugins (Flash)
- Upgraded to Cesium 1.22 which provides new advanced shadows (see pictures)
- Implemented an orientation control mode for mobiles (tilting phone to control aircraft)
- Redesigned the UI with mobile support in mind (responsive) and to get rid of plugin legacy (chat messages are now shown as overlay)
- Improved hot air balloon simulation with a a new atmospheric model (air temp and pressure)