Starfield updated to self-generate stars from random number seed.

Stars no longer load from a text file, but self generate instead (speed
improvement - see interface/src/starfield/Generator.h).

Switching between loading from server and locally generating is defined
by STARFIELD_GENERATE_RANDOM in interface/src/Application.h

getFileLoaded() in interface/src/Stars.h changed to getStarsLoaded()
for clarity (as file will not be loaded if generating stars).