Center default detector layout around GPS

GPS as 0, 0 instead of center of mass (for default 4 detector station)
Fix 508 rotation
Corrected 502 diamond shape layout
Add functions to calculate center of mass for station and cluster
Add subclass for a cluster with a single 2 detector station
Add subclass for a cluster with a single diamond station
Remove unused keyword
Has division from future, no dots needed
Add tests for center of mass calculation
Merge branch 'station-layout'

Add subclasses for 2 detector stations and diamond layout
Add functions to calculate center of mass for stations or clusters
'Default' 4 detector layout now has (0,0) at GPS location instead of detector 2