use M_.occbin.filter_initial_state to perform smoothers running particles from smoothed estimate of states in t=0

new utility to check that the updated states in t-1 and shocks in t always deliver the same regime as per PKF

occbin.pkf_conditional_density.m becomes the main wrapper for PPF steps in KF. maybe it should be renamed

use option to set the threshold for using PKF updated state. default=1, i.e. we switch to PKF updated state only if 100% of the updated particles belong to base regime

allow using particle filter likelihood at the beginning of the filter. filter will automatically turn to standard PKF once back to base regime

- trap case when the PKF update engine does not find a solution

- changed use_relaxation behavior, to match more closely the old one (but more efficiently)

trap the case when the occbin simulation does not converge (should only happen when first_period_occbin_update>1)

initialize undocumented options that would otherwise lead to a crash in occbin.shock_decomposition (unrecognized field name)

Manually resolved conflicts from 4.7 JRC branch