added version detection based on filename of first file in folder

- alternatives would have been using the id in the netCDF file
  but this did not work already with WARP5.5R21 but might be more
  stable in the future. Unless the naming conventions are changed
  this method should work for the next versions
added SWI calculation example
added changes for version 0.2.5
import modules from pyresample explicitly
changed pandas requirements since ismn reader breaks with verison 0.15.2
Merge pull request #19 from TUW-GEO/develop

Develop to master for version 0.2.5