Add tests for units and particles in CORSIKA module
Update gpstime to work for entire HiSPARC period

Added leap second from January 1, 2006
This makes the script work for dates till January 1, 1999
Added tests for gpstime module
More reasonable timestamps

Timestamp long(1e9) is on September 9, 2001
Which is within the HiSPARC operational timespan