ft_databrowser should have cfg.nirsscale option

[robertoostenveld]

as discussed with @helenacockx. Similar as the other channel types

% The following options for the scaling of the EEG, EOG, ECG, EMG and MEG channels is
% optional and can be used to bring the absolute numbers of the different channel
% types in the same range (e.g. fT and uV). The channel types are determined from the
% input data using FT_CHANNELSELECTION.
%   cfg.eegscale                = number, scaling to apply to the EEG channels prior to display
%   cfg.eogscale                = number, scaling to apply to the EOG channels prior to display
%   cfg.ecgscale                = number, scaling to apply to the ECG channels prior to display
%   cfg.emgscale                = number, scaling to apply to the EMG channels prior to display
%   cfg.megscale                = number, scaling to apply to the MEG channels prior to display
%   cfg.gradscale               = number, scaling to apply to the MEG gradiometer channels prior to display (in addition to the cfg.megscale factor)
%   cfg.magscale                = number, scaling to apply to the MEG magnetometer channels prior to display (in addition to the cfg.megscale factor)
%   cfg.mychanscale             = number, scaling to apply to the channels specified in cfg.mychan
%   cfg.mychan                  = Nx1 cell-array with selection of channels
%   cfg.chanscale               = Nx1 vector with scaling factors, one per channel specified in cfg.channel
%   cfg.compscale               = string, 'global' or 'local', defines whether the colormap for the topographic scaling is applied per topography or on all visualized components (default 'global')
%

[robertoostenveld]

all plotting functions that support this now also include it in their documentation