fix bad handling of remote params, resulting in wrong information given in them in case of received INVITE without SDP

Do not use anymore nb_streams but SAL_MEDIA_DESCRIPTION_MAX_STREAMS and skip inactive ones because active streams won't be at the start of the array anymore

fix bugs in Paused state management. It was possible to transition from Paused to PausedByRemote, which actually breaks the Paused state, and eventually allows the pauser to be resumed by the paused.

rename LinphoneCallParamsMediaDirection into LinphoneMediaDirection, as it has no reason to be attached to LinphoneCallParams and could be re-used in other contexts.