Update -cmninit parameter when CMN is updated

[dhdaines]

This allows a simple form of enrollment or channel adaptation - the string representation of the current live cepstral mean, as passed to -cmninit, can always be accessed through the configuration object in the decoder, e.g.:

printf("current cepstral mean is %s\n", cmd_ln_str_r(ps_get_config(decoder), "-cmninit"));

In addition, ps_reinit_fe() has been renamed to ps_reinit_feat() so as to include modifications to -cmninit, VTLN, and other pertinent parameters.

[lenzo-ka]

LGTM with minor notes