find info about channel (gain, bandpass) for a given channel in a specific session.
SYNOPSIS
function [exists, infos, isGround] = getChannelInfo( headerInfos, sessionID, channelNr )
DESCRIPTION
find info about channel (gain, bandpass) for a given channel in a specific session.
reads the headerInfos.mat file that needs to be created first (and extended for every session)
urut/june06