Add PCAL to DARM arm signs

Jeff requests:

I suggest we put in a new merge request that does the following in calcs.CALCSModel.compute_epics_records():

• Add two new variables to the parameter file called pcalx_2_darm_act_sign = +1 and pcaly_2_darm_act_sign = -1
• By default, set ref_pcal_2_darm_act_sign = pcaly_2_darm_act_sign,
• To allow for backward compatibility, set defaults for these values within this method (and anywhere else we end up using it),
• Then in this method, multiply in the new variables,

PCAL_OVER_DARM_X_COMPARE_CORRECTION = (
            self.pcal.pcalx_2_darm_act_sign * 
            pcal_correction[6] /
            self.pcal.ref_pcal_2_darm_act_sign /
            darm_advance[6])
        PCAL_OVER_DARM_Y_COMPARE_CORRECTION = (
            self.pcal.pcaly_2_darm_act_sign * 
            * pcal_correction[7] /
            self.pcal.ref_pcal_2_darm_act_sign /
            darm_advance[7])

Or something along these lines