Add FID graph calculation to MRzeroCore

[SWeinmueller]

For higher FA "execute_graph(graph, seq, obj, min_emitted_signal=1, min_latent_signal=1)" can give different result than really the FID graph

[mzaiss]

what?
why and when exactly?

[SWeinmueller]

FID graph: Really the path of the type of the pulse is simulated, i. e. z0 and 'z+' state (EXCIT) and z0 and '-+' (REFOC)
"execute_graph(graph, seq, obj, min_emitted_signal=1, min_latent_signal=1)": Signal with highest influence. If z magnetisation is small (high FA in GRE), other paths could be more relevant