[NL] Make Time constructor explicit, TimeStepAlgorithm::{begin,end} return Time

NumLib/TimeStepping/Algorithms/FixedTimeStepping.cpp

NumLib/TimeStepping/Algorithms/FixedTimeStepping.h

NumLib/TimeStepping/Algorithms/TimeStepAlgorithm.cpp

NumLib/TimeStepping/Algorithms/TimeStepAlgorithm.h

NumLib/TimeStepping/Time.h

ProcessLib/CreateTimeLoop.cpp

ProcessLib/ProcessData.h

Tests/NumLib/TestFixedTimeStepping.cpp

Tests/NumLib/TestTimeSteppingFixed.cpp

Tests/NumLib/TestTimeSteppingIterationNumber.cpp

Tests/NumLib/TimeSteppingTestingTools.h

Tests/ProcessLib/TestProcessLibOutput.cpp