Add Agilent33600a Arb waveform upload

[DanielTreuherz]

Added arb waveform upload

Example usage

    num_points = 4e6
    sample_rate = 1e6
    t = np.linspace(0, 1, int(num_points))
    
    sig = np.sin(2 * np.pi * 50 * t) 
    sig /= np.max(np.abs(sig))

    
    awg = Agilent33600A(ip)

    awg.upload_custom_waveform('test', sig)
    awg.set_function('arb')
    awg.set_sample_rate(sample_rate)

    awg.close()