Set fast preview scan parameters for galvos in the system settings YAML

[raacampbell]

Currently we have in takeRapidPrview the following

% This is a nasty hack for ensuring fast scanning galvos proceeds at a reasonable frame rate
    if isa(obj.scanner, 'SIBT') && strcmp(obj.scanner.scannerType,'linear')
        obj.scanner.hC.hScan2D.pixelBinFactor=12;
        obj.scanner.hC.hScan2D.sampleRate=1.25E6;
    end

Those settings should be in the systems settings YAML so they can be changed by the superuser.