Fixing plotting issues as well as usage of reference value

This is my proposal to fix the issues I found on the scanner while testing with the latest snapshot (6.1-SNAPSHOT).

• Plots were not updated correctly. After the refactoring, the number of measurements taken was not being correctly updated.
• Reference value on the PV list was ignored and instead the value from EPICS was used.

Before releasing a new version, we first need to agree on releasing OXAL-6.1

assigned to @yngvelevinsen

Thanks! Looks good to me

merged

mentioned in commit 5397fad6