Adding DLL-Project for Solver
Adding Particles into Solver as datatype
Exchanging old Prticles struct through external Particles struct in the Solver library
backup
bruteForce() moved to Solver::Euler()
constants.h added to Solver
constants implemented
constants.h removed from ParticleUI
use constants from Solver
Cleaning and deleting unused stuff
DAYS_PER_YEAR added
adjusting small things
Introducing EulerStep Function
Unit-Test library added for Solver
first test of EulerStep succesfully running
Merge branch 'develop' into feature/Refactoring

Conflicts:
	Particles/Particles.pro.user
prepare Particles for test of Solver::Euler()
Test runs as expected and fails
test still not passed
Intermediate checkin just for backup and a manual calculation for designing the euler test case