[SIGMON-428] Corrected slope calculation in notebook

Context

• story: https://its.cern.ch/jira/browse/SIGMON-119
• task: https://its.cern.ch/jira/browse/SIGMON-428
• lhc-sm-api review: lhc-sm-api!213 (merged)

What was done

• appropriate qps thresholds used
• workaround for the buggy algorithm removed
• lims for plots adjusted

TODO

• propagate to other notebooks (?) - IT PIC2, IT FPA,  600A FPAs, IPD FPA, IPD PLI2.f2, IPQ PLI2.f3 and IT PLI3.f6

QA

• no sonar, no tests, notebooks 😉

Review objectives

• assessment of code functionality
• assessment of code quality
• identifying potential refactorings / logic common to other projects
• knowledge sharing