Remove rt.bmr.sum from the rt.bmr beacon processor and change the rt.bmr.index logic to qualified names

[Patrick-Eichhorn]

The sum of the single rt.bmr values leads to an incorrect result. All values refer to the first startTime value: during summing up, times are counted multiple times from the start value.

Currently, the single values can be accessed via the index logic (f.e. rt.bmr.0 stands for startTime). To make the access more applicable and explicit, a name mapping needs to be implemented for the value expression settings. (f.e rt.bmr.startTime)