Substitutes DEBIAN_STYLE_LIBEXEC flag and manages location and name of lib and libexec folders on Debian/Ubuntu-based systems

there are now three startup files; ost_startup.py (former init_cl.py) initializes non-gui ost; dng_startup (former init.py) initializes dng; and gosty_startup initializes gosty (some issues remain what to put into dng_startup as opposed to gosty_startup). also, files are now properly placed into site-packages/ost (on osx and linux)

Instead of creating a lib/openstructure subdirectory containing
all ost modules, use lib/python$MAJOR.$MINOR/site-packages. This
follows more closely what other projects are doing. The main
motivation, however is to simplify deploment of tools built on
OpenStructure.

fixed python version in ost_config PYTHONPATH

1. Option to move libexec to lib/openstructure/libexec
2. Gosty moved to libexec

changed cmake scripts to allow building as subproject / moved common configuration from startup scripts to separate script

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@1878 5a81b35b-ba03-0410-adc8-b2c5c5119f08

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@1742 5a81b35b-ba03-0410-adc8-b2c5c5119f08