updated to version 3

includes some fixes to backgrounds new shiny shaders and railgun frigate.

updated version number to 0.21

Made shipyard sensor modules buildable.

- PDS system ingame icons got removed because of bloat.

- 0.1 actually missed sensor subsystems from carriers and stations.

- Put back those original skirmish settings(i had modified em because i wanted to make starting fleetsize option which never worked properly)