Allow setting initial state for Kalman filter

doc/manual/source/the-model-file.rst

matlab/DsgeSmoother.m

matlab/dsge_likelihood.m

matlab/initial_estimation_checks.m

matlab/missing_DiffuseKalmanSmootherH1_Z.m

matlab/missing_DiffuseKalmanSmootherH3_Z.m

preprocessor

tests/Makefile.am

tests/kalman_initial_state/fs2000_common.inc

tests/kalman_initial_state/fs2000_kalman_initial.mod

tests/kalman_initial_state/fs2000_kalman_initial_2_lag.mod

tests/kalman_initial_state/fs2000_kalman_initial_xfail.mod

...n_initial_state/fs2000_ns_smoother_only_initial_state.mod

...lman_initial_state/fs2000_smoother_only_initial_state.mod