Fix test dac linearity

This will fix a bug in the analysis and plotting for the 'test_dac_linearity' where 'start_column', 'stop_column', etc. are not set in the 'run_config', which leads to a failure in the analysis. Additionally a bug in the linear fitting ad plotting is fixed which used all measured data in order to estimate the slope of the dac leading to large discrepancies of the real dac slope. Now saturation effects at the edges are ignored. Additionally the proper usage of 'scan_param_id' for 'test_dac_linearity' is implemented.