Added reference forces and energies from ewald to dna_water system
neaer typo in FCSInterface.c corrected (print statement)
neaer typo in FCSInterface.c corrected (print statement)
FCS_2_SQRTPI in documentation file interface.tex set to value of FCSDefinitions.h and typo corrected

removal of constants like M_E from lib/p3m/utils.h and lib/p3m/error_estimate.c to prevent redundancy and improve maintenance. Please use the constants from FCSDefinitions.h like FCS_E. current usages were replaced by FCS_constants

Signed-off-by: Gabriel Sichardt <gabriel@icp.uni-stuttgart.de>
Merge branch 'master' of https://github.com/g-sichardt/scafacos
include for FCSDefinitions.h added in error_estimate.c and utils.h, currently surrounded with ifndef.
Merge branch 'master' of https://github.com/g-sichardt/scafacos

Conflicts:
	test/generic/systems/3d-periodic/dna_water_15543.xml.gz
use FCS Constants and add an assertation at the beginning of the run function.