Removed source file astro.f90, moving contents to astronomy library libTheSky

* Removed source file astro.f90; moving contents to astronomy library libTheSky:
  * contents of astro.f90 are being moved to libTheSky
  * functions calcgmst(), airmass(), airmass_ext()
  * libTheSky is an astronomy library, hence a more natural place for these procedures
  * you can find it at http://libthesky.sourceforge.net
CMake: added dependency of static lib on shared lib for stable multithread make

* CMake: added dependency of static lib on shared lib for stable multithread make:
  * otherwise, both threads can pour data into the code_version file simultaneously